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 $117.44   12.466%   $132.0801   $132.08   $132.10   $132.10  
  Purchase #2 $246.34   8.427%   $267.0991   $267.10   $267.10   $267.10  
  Purchase #3 $67.90   8.189%   $73.4603   $73.46   $73.45   $73.50  
  Purchase #4 $42.29   9.172%   $46.1688   $46.17   $46.15   $46.20  
  Purchase #5 $202.52   6.338%   $215.3557   $215.36   $215.35   $215.40  
  Purchase #6 $135.72   7.207%   $145.5013   $145.50   $145.50   $145.50  
  Purchase #7 $64.79   12.227%   $72.7119   $72.71   $72.70   $72.70  
  7 purchase totals = $877.00       $952.3772   $952.38   $952.35   $952.50