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 $166.89   5.776%   $176.5296   $176.53   $176.55   $176.50  
  Purchase #2 $105.50   11.144%   $117.2569   $117.26   $117.25   $117.30  
  Purchase #3 $146.55   3.153%   $151.1707   $151.17   $151.15   $151.20  
  Purchase #4 $220.39   11.499%   $245.7326   $245.73   $245.75   $245.70  
  Purchase #5 $176.52   10.347%   $194.7845   $194.78   $194.80   $194.80  
  Purchase #6 $135.85   13.801%   $154.5987   $154.60   $154.60   $154.60  
  Purchase #7 $24.87   10.551%   $27.494   $27.49   $27.50   $27.50  
  7 purchase totals = $976.57       $1,067.5670   $1,067.56   $1,067.60   $1,067.60