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 $122.41   3.143%   $126.2573   $126.26   $126.25   $126.30  
  Purchase #2 $239.86   5.621%   $253.3425   $253.34   $253.35   $253.30  
  Purchase #3 $174.67   4.486%   $182.5057   $182.51   $182.50   $182.50  
  Purchase #4 $78.45   3.177%   $80.9424   $80.94   $80.95   $80.90  
  Purchase #5 $6.26   4.251%   $6.5261   $6.53   $6.55   $6.50  
  Purchase #6 $75.38   5.396%   $79.4475   $79.45   $79.45   $79.40  
  Purchase #7 $136.56   4.185%   $142.275   $142.28   $142.30   $142.30  
  7 purchase totals = $833.59       $871.2965   $871.31   $871.35   $871.20