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 $169.65   12.669%   $191.143   $191.14   $191.15   $191.10  
  Purchase #2 $248.94   11.837%   $278.407   $278.41   $278.40   $278.40  
  Purchase #3 $58.39   13.677%   $66.376   $66.38   $66.40   $66.40  
  Purchase #4 $182.60   3.585%   $189.1462   $189.15   $189.15   $189.10  
  Purchase #5 $12.33   4.131%   $12.8394   $12.84   $12.85   $12.80  
  Purchase #6 $22.50   11.424%   $25.0704   $25.07   $25.05   $25.10  
  Purchase #7 $206.44   3.463%   $213.589   $213.59   $213.60   $213.60  
  7 purchase totals = $900.85       $976.5710   $976.58   $976.60   $976.50