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 $65.97   11.591%   $73.6166   $73.62   $73.60   $73.60  
  Purchase #2 $67.76   4.601%   $70.8776   $70.88   $70.90   $70.90  
  Purchase #3 $107.33   4.350%   $111.9989   $112.00   $112.00   $112.00  
  Purchase #4 $121.27   7.827%   $130.7618   $130.76   $130.75   $130.80  
  Purchase #5 $146.32   6.804%   $156.2756   $156.28   $156.30   $156.30  
  Purchase #6 $243.73   5.790%   $257.842   $257.84   $257.85   $257.80  
  Purchase #7 $137.90   10.277%   $152.072   $152.07   $152.05   $152.10  
  7 purchase totals = $890.28       $953.4445   $953.45   $953.45   $953.50