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 $130.96   11.682%   $146.2587   $146.26   $146.25   $146.30  
  Purchase #2 $149.45   11.479%   $166.6054   $166.61   $166.60   $166.60  
  Purchase #3 $163.59   9.781%   $179.5907   $179.59   $179.60   $179.60  
  Purchase #4 $65.41   5.330%   $68.8964   $68.90   $68.90   $68.90  
  Purchase #5 $111.91   5.455%   $118.0147   $118.01   $118.00   $118.00  
  Purchase #6 $141.75   8.637%   $153.9929   $153.99   $154.00   $154.00  
  Purchase #7 $67.76   3.866%   $70.3796   $70.38   $70.40   $70.40  
  7 purchase totals = $830.83       $903.7384   $903.74   $903.75   $903.80