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 $202.96   11.622%   $226.548   $226.55   $226.55   $226.50  
  Purchase #2 $18.94   12.794%   $21.3632   $21.36   $21.35   $21.40  
  Purchase #3 $56.65   11.824%   $63.3483   $63.35   $63.35   $63.30  
  Purchase #4 $39.47   11.710%   $44.0919   $44.09   $44.10   $44.10  
  Purchase #5 $195.54   5.121%   $205.5536   $205.55   $205.55   $205.60  
  Purchase #6 $238.47   10.405%   $263.2828   $263.28   $263.30   $263.30  
  Purchase #7 $69.40   8.374%   $75.2116   $75.21   $75.20   $75.20  
  7 purchase totals = $821.43       $899.3994   $899.39   $899.40   $899.40