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 $202.82   10.424%   $223.962   $223.96   $223.95   $224.00  
  Purchase #2 $146.33   6.353%   $155.6263   $155.63   $155.65   $155.60  
  Purchase #3 $15.50   10.129%   $17.07   $17.07   $17.05   $17.10  
  Purchase #4 $242.35   6.421%   $257.9113   $257.91   $257.90   $257.90  
  Purchase #5 $170.68   9.847%   $187.4869   $187.49   $187.50   $187.50  
  Purchase #6 $161.80   6.409%   $172.1698   $172.17   $172.15   $172.20  
  Purchase #7 $124.96   13.216%   $141.4747   $141.47   $141.45   $141.50  
  7 purchase totals = $1,064.44       $1,155.7010   $1,155.70   $1,155.65   $1,155.80