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 $67.82   11.490%   $75.6125   $75.61   $75.60   $75.60  
  Purchase #2 $219.75   9.206%   $239.9802   $239.98   $240.00   $240.00  
  Purchase #3 $239.53   13.193%   $271.1312   $271.13   $271.15   $271.10  
  Purchase #4 $226.60   13.271%   $256.6721   $256.67   $256.65   $256.70  
  Purchase #5 $68.71   7.434%   $73.8179   $73.82   $73.80   $73.80  
  Purchase #6 $205.42   13.105%   $232.3403   $232.34   $232.35   $232.30  
  Purchase #7 $80.45   4.380%   $83.9737   $83.97   $83.95   $84.00  
  7 purchase totals = $1,108.28       $1,233.5279   $1,233.52   $1,233.50   $1,233.50