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 $91.76   13.533%   $104.1779   $104.18   $104.20   $104.20  
  Purchase #2 $227.32   6.276%   $241.5866   $241.59   $241.60   $241.60  
  Purchase #3 $244.30   10.320%   $269.5118   $269.51   $269.50   $269.50  
  Purchase #4 $106.73   6.456%   $113.6205   $113.62   $113.60   $113.60  
  Purchase #5 $60.72   12.576%   $68.3561   $68.36   $68.35   $68.40  
  Purchase #6 $57.72   4.743%   $60.4577   $60.46   $60.45   $60.50  
  Purchase #7 $145.89   13.271%   $165.2511   $165.25   $165.25   $165.30  
  7 purchase totals = $934.44       $1,022.9617   $1,022.97   $1,022.95   $1,023.10