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 $194.58   11.534%   $217.0229   $217.02   $217.00   $217.00  
  Purchase #2 $95.55   3.485%   $98.8799   $98.88   $98.90   $98.90  
  Purchase #3 $123.54   8.638%   $134.2114   $134.21   $134.20   $134.20  
  Purchase #4 $109.76   5.648%   $115.9592   $115.96   $115.95   $116.00  
  Purchase #5 $184.60   5.194%   $194.1881   $194.19   $194.20   $194.20  
  Purchase #6 $150.80   8.120%   $163.045   $163.05   $163.05   $163.00  
  Purchase #7 $35.97   6.330%   $38.2469   $38.25   $38.25   $38.20  
  7 purchase totals = $894.80       $961.5534   $961.56   $961.55   $961.50