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 $130.35   7.500%   $140.1263   $140.13   $140.15   $140.10  
  Purchase #2 $24.50   5.429%   $25.8301   $25.83   $25.85   $25.80  
  Purchase #3 $63.77   6.601%   $67.9795   $67.98   $68.00   $68.00  
  Purchase #4 $147.81   11.366%   $164.6101   $164.61   $164.60   $164.60  
  Purchase #5 $93.76   7.717%   $100.9955   $101.00   $101.00   $101.00  
  Purchase #6 $27.26   9.327%   $29.8025   $29.80   $29.80   $29.80  
  Purchase #7 $42.40   13.302%   $48.04   $48.04   $48.05   $48.00  
  7 purchase totals = $529.85       $577.3840   $577.39   $577.45   $577.30