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 $93.53   4.493%   $97.7323   $97.73   $97.75   $97.70  
  Purchase #2 $187.42   3.856%   $194.6469   $194.65   $194.65   $194.60  
  Purchase #3 $13.66   4.592%   $14.2873   $14.29   $14.30   $14.30  
  Purchase #4 $154.97   6.205%   $164.5859   $164.59   $164.60   $164.60  
  Purchase #5 $160.94   3.776%   $167.0171   $167.02   $167.00   $167.00  
  Purchase #6 $234.27   6.598%   $249.7271   $249.73   $249.75   $249.70  
  Purchase #7 $11.61   13.792%   $13.2113   $13.21   $13.20   $13.20  
  7 purchase totals = $856.40       $901.2079   $901.22   $901.25   $901.10