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 $164.62   13.246%   $186.4256   $186.43   $186.45   $186.40  
  Purchase #2 $91.52   11.838%   $102.3541   $102.35   $102.35   $102.40  
  Purchase #3 $136.67   13.852%   $155.6015   $155.60   $155.60   $155.60  
  Purchase #4 $84.51   3.306%   $87.3039   $87.30   $87.30   $87.30  
  Purchase #5 $111.97   4.213%   $116.6873   $116.69   $116.70   $116.70  
  Purchase #6 $65.76   8.406%   $71.2878   $71.29   $71.30   $71.30  
  Purchase #7 $229.76   13.769%   $261.3957   $261.40   $261.40   $261.40  
  7 purchase totals = $884.81       $981.0559   $981.06   $981.10   $981.10