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 $154.45   7.362%   $165.8206   $165.82   $165.80   $165.80  
  Purchase #2 $241.95   5.380%   $254.9669   $254.97   $254.95   $255.00  
  Purchase #3 $58.36   7.114%   $62.5117   $62.51   $62.50   $62.50  
  Purchase #4 $123.54   7.255%   $132.5028   $132.50   $132.50   $132.50  
  Purchase #5 $117.49   6.380%   $124.9859   $124.99   $125.00   $125.00  
  Purchase #6 $45.73   8.212%   $49.4853   $49.49   $49.50   $49.50  
  Purchase #7 $50.91   6.765%   $54.3541   $54.35   $54.35   $54.40  
  7 purchase totals = $792.43       $844.6273   $844.63   $844.60   $844.70