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 $244.36   12.617%   $275.1909   $275.19   $275.20   $275.20  
  Purchase #2 $204.72   9.713%   $224.6045   $224.60   $224.60   $224.60  
  Purchase #3 $47.83   4.701%   $50.0785   $50.08   $50.10   $50.10  
  Purchase #4 $24.97   5.753%   $26.4065   $26.41   $26.40   $26.40  
  Purchase #5 $224.41   13.755%   $255.2776   $255.28   $255.30   $255.30  
  Purchase #6 $77.26   5.644%   $81.6206   $81.62   $81.60   $81.60  
  Purchase #7 $215.94   10.195%   $237.9551   $237.96   $237.95   $238.00  
  7 purchase totals = $1,039.49       $1,151.1337   $1,151.14   $1,151.15   $1,151.20