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 $9.97   9.873%   $10.9543   $10.95   $10.95   $11.00  
  Purchase #2 $94.59   5.731%   $100.011   $100.01   $100.00   $100.00  
  Purchase #3 $201.60   3.335%   $208.3234   $208.32   $208.30   $208.30  
  Purchase #4 $8.31   3.569%   $8.6066   $8.61   $8.60   $8.60  
  Purchase #5 $7.80   3.174%   $8.0476   $8.05   $8.05   $8.00  
  Purchase #6 $46.97   5.571%   $49.5867   $49.59   $49.60   $49.60  
  Purchase #7 $203.42   13.435%   $230.7495   $230.75   $230.75   $230.70  
  7 purchase totals = $572.66       $616.2791   $616.28   $616.25   $616.20