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 $218.82   10.541%   $241.8858   $241.89   $241.90   $241.90  
  Purchase #2 $241.73   6.734%   $258.0081   $258.01   $258.00   $258.00  
  Purchase #3 $14.70   10.425%   $16.2325   $16.23   $16.25   $16.20  
  Purchase #4 $104.73   7.267%   $112.3407   $112.34   $112.35   $112.30  
  Purchase #5 $191.74   6.306%   $203.8311   $203.83   $203.85   $203.80  
  Purchase #6 $76.74   7.487%   $82.4855   $82.49   $82.50   $82.50  
  Purchase #7 $151.35   4.477%   $158.1259   $158.13   $158.15   $158.10  
  7 purchase totals = $999.81       $1,072.9096   $1,072.92   $1,073.00   $1,072.80