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 $59.70   13.211%   $67.587   $67.59   $67.60   $67.60  
  Purchase #2 $29.89   9.218%   $32.6453   $32.65   $32.65   $32.60  
  Purchase #3 $221.46   7.448%   $237.9543   $237.95   $237.95   $238.00  
  Purchase #4 $209.44   10.627%   $231.6972   $231.70   $231.70   $231.70  
  Purchase #5 $70.71   3.596%   $73.2527   $73.25   $73.25   $73.30  
  Purchase #6 $154.86   11.283%   $172.3329   $172.33   $172.35   $172.30  
  Purchase #7 $46.42   6.629%   $49.4972   $49.50   $49.50   $49.50  
  7 purchase totals = $792.48       $864.9666   $864.97   $865.00   $865.00