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 $56.87   9.779%   $62.4313   $62.43   $62.45   $62.40  
  Purchase #2 $182.86   11.766%   $204.3753   $204.38   $204.40   $204.40  
  Purchase #3 $126.33   4.184%   $131.6156   $131.62   $131.60   $131.60  
  Purchase #4 $211.32   7.282%   $226.7083   $226.71   $226.70   $226.70  
  Purchase #5 $124.91   4.563%   $130.6096   $130.61   $130.60   $130.60  
  Purchase #6 $85.90   6.189%   $91.2164   $91.22   $91.20   $91.20  
  Purchase #7 $130.82   3.590%   $135.5164   $135.52   $135.50   $135.50  
  7 purchase totals = $919.01       $982.4729   $982.49   $982.45   $982.40