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 $68.60   11.679%   $76.6118   $76.61   $76.60   $76.60  
  Purchase #2 $160.95   8.255%   $174.2364   $174.24   $174.25   $174.20  
  Purchase #3 $113.31   5.626%   $119.6848   $119.68   $119.70   $119.70  
  Purchase #4 $211.85   8.403%   $229.6518   $229.65   $229.65   $229.70  
  Purchase #5 $10.89   8.680%   $11.8353   $11.84   $11.85   $11.80  
  Purchase #6 $225.85   8.390%   $244.7988   $244.80   $244.80   $244.80  
  Purchase #7 $114.26   12.863%   $128.9573   $128.96   $128.95   $129.00  
  7 purchase totals = $905.71       $985.7762   $985.78   $985.80   $985.80