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 $81.53   8.628%   $88.5644   $88.56   $88.55   $88.60  
  Purchase #2 $146.78   10.128%   $161.6459   $161.65   $161.65   $161.60  
  Purchase #3 $24.75   5.152%   $26.0251   $26.03   $26.05   $26.00  
  Purchase #4 $42.26   7.506%   $45.432   $45.43   $45.45   $45.40  
  Purchase #5 $98.69   12.662%   $111.1861   $111.19   $111.20   $111.20  
  Purchase #6 $145.75   4.548%   $152.3787   $152.38   $152.40   $152.40  
  Purchase #7 $61.39   9.219%   $67.0495   $67.05   $67.05   $67.00  
  7 purchase totals = $601.15       $652.2817   $652.29   $652.35   $652.20