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 $84.67   12.194%   $94.9947   $94.99   $95.00   $95.00  
  Purchase #2 $180.73   7.591%   $194.4492   $194.45   $194.45   $194.40  
  Purchase #3 $195.75   3.191%   $201.9964   $202.00   $202.00   $202.00  
  Purchase #4 $182.68   6.197%   $194.0007   $194.00   $194.00   $194.00  
  Purchase #5 $118.51   13.118%   $134.0561   $134.06   $134.05   $134.10  
  Purchase #6 $46.76   5.722%   $49.4356   $49.44   $49.45   $49.40  
  Purchase #7 $10.80   9.377%   $11.8127   $11.81   $11.80   $11.80  
  7 purchase totals = $819.90       $880.7454   $880.75   $880.75   $880.70