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 $53.85   7.618%   $57.9523   $57.95   $57.95   $58.00  
  Purchase #2 $116.37   3.622%   $120.5849   $120.58   $120.60   $120.60  
  Purchase #3 $57.26   12.459%   $64.394   $64.39   $64.40   $64.40  
  Purchase #4 $239.31   13.798%   $272.33   $272.33   $272.35   $272.30  
  Purchase #5 $219.30   6.810%   $234.2343   $234.23   $234.25   $234.20  
  Purchase #6 $5.33   12.695%   $6.0066   $6.01   $6.00   $6.00  
  Purchase #7 $125.66   8.262%   $136.042   $136.04   $136.05   $136.00  
  7 purchase totals = $817.08       $891.5441   $891.53   $891.60   $891.50