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 $43.41   7.314%   $46.585   $46.59   $46.60   $46.60  
  Purchase #2 $34.84   3.155%   $35.9392   $35.94   $35.95   $35.90  
  Purchase #3 $119.48   12.389%   $134.2824   $134.28   $134.30   $134.30  
  Purchase #4 $209.33   8.123%   $226.3339   $226.33   $226.35   $226.30  
  Purchase #5 $161.49   5.217%   $169.9149   $169.91   $169.90   $169.90  
  Purchase #6 $123.93   4.721%   $129.7807   $129.78   $129.80   $129.80  
  Purchase #7 $88.61   7.837%   $95.5544   $95.55   $95.55   $95.60  
  7 purchase totals = $781.09       $838.3905   $838.38   $838.45   $838.40