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 $60.68   10.341%   $66.9549   $66.95   $66.95   $67.00  
  Purchase #2 $76.28   8.760%   $82.9621   $82.96   $82.95   $83.00  
  Purchase #3 $62.86   7.409%   $67.5173   $67.52   $67.50   $67.50  
  Purchase #4 $132.57   9.662%   $145.3789   $145.38   $145.40   $145.40  
  Purchase #5 $137.49   8.303%   $148.9058   $148.91   $148.90   $148.90  
  Purchase #6 $221.48   7.344%   $237.7455   $237.75   $237.75   $237.70  
  Purchase #7 $39.44   11.185%   $43.8514   $43.85   $43.85   $43.90  
  7 purchase totals = $730.80       $793.3159   $793.32   $793.30   $793.40