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 $245.66   6.560%   $261.7753   $261.78   $261.80   $261.80  
  Purchase #2 $24.37   4.224%   $25.3994   $25.40   $25.40   $25.40  
  Purchase #3 $104.58   11.638%   $116.751   $116.75   $116.75   $116.80  
  Purchase #4 $42.77   6.425%   $45.518   $45.52   $45.50   $45.50  
  Purchase #5 $244.99   3.589%   $253.7827   $253.78   $253.80   $253.80  
  Purchase #6 $104.39   4.633%   $109.2264   $109.23   $109.25   $109.20  
  Purchase #7 $99.26   7.793%   $106.9953   $107.00   $107.00   $107.00  
  7 purchase totals = $866.02       $919.4481   $919.46   $919.50   $919.50