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 $228.34   11.219%   $253.9575   $253.96   $253.95   $254.00  
  Purchase #2 $212.86   5.162%   $223.8478   $223.85   $223.85   $223.80  
  Purchase #3 $225.71   3.754%   $234.1832   $234.18   $234.20   $234.20  
  Purchase #4 $247.83   9.538%   $271.468   $271.47   $271.45   $271.50  
  Purchase #5 $120.47   9.737%   $132.2002   $132.20   $132.20   $132.20  
  Purchase #6 $103.86   4.854%   $108.9014   $108.90   $108.90   $108.90  
  Purchase #7 $210.33   12.168%   $235.923   $235.92   $235.90   $235.90  
  7 purchase totals = $1,349.40       $1,460.4811   $1,460.48   $1,460.45   $1,460.50