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 $56.96   11.105%   $63.2854   $63.29   $63.30   $63.30  
  Purchase #2 $157.43   9.682%   $172.6724   $172.67   $172.65   $172.70  
  Purchase #3 $212.33   11.650%   $237.0664   $237.07   $237.05   $237.10  
  Purchase #4 $123.80   6.757%   $132.1652   $132.17   $132.15   $132.20  
  Purchase #5 $102.76   10.424%   $113.4717   $113.47   $113.45   $113.50  
  Purchase #6 $32.80   11.350%   $36.5228   $36.52   $36.50   $36.50  
  Purchase #7 $128.96   11.136%   $143.321   $143.32   $143.30   $143.30  
  7 purchase totals = $815.04       $898.5049   $898.51   $898.40   $898.60