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 $171.40   13.550%   $194.6247   $194.62   $194.60   $194.60  
  Purchase #2 $62.34   12.185%   $69.9361   $69.94   $69.95   $69.90  
  Purchase #3 $27.64   11.737%   $30.8841   $30.88   $30.90   $30.90  
  Purchase #4 $221.78   3.323%   $229.1497   $229.15   $229.15   $229.10  
  Purchase #5 $54.89   7.311%   $58.903   $58.90   $58.90   $58.90  
  Purchase #6 $148.94   6.653%   $158.849   $158.85   $158.85   $158.80  
  Purchase #7 $96.27   6.514%   $102.541   $102.54   $102.55   $102.50  
  7 purchase totals = $783.26       $844.8876   $844.88   $844.90   $844.70