Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.47   11.486%   $227.9554   $227.96   $227.95   $228.00  
  Purchase #2 $104.92   13.234%   $118.8051   $118.81   $118.80   $118.80  
  Purchase #3 $112.39   13.323%   $127.3637   $127.36   $127.35   $127.40  
  Purchase #4 $155.75   7.227%   $167.0061   $167.01   $167.00   $167.00  
  Purchase #5 $198.63   13.479%   $225.4033   $225.40   $225.40   $225.40  
  Purchase #6 $184.91   9.873%   $203.1662   $203.17   $203.15   $203.20  
  Purchase #7 $167.35   10.405%   $184.7628   $184.76   $184.75   $184.80  
  7 purchase totals = $1,128.42       $1,254.4626   $1,254.47   $1,254.40   $1,254.60