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 $48.88   11.622%   $54.5608   $54.56   $54.55   $54.60  
  Purchase #2 $192.76   10.328%   $212.6683   $212.67   $212.65   $212.70  
  Purchase #3 $143.47   9.626%   $157.2804   $157.28   $157.30   $157.30  
  Purchase #4 $124.88   8.516%   $135.5148   $135.51   $135.50   $135.50  
  Purchase #5 $17.72   3.301%   $18.3049   $18.30   $18.30   $18.30  
  Purchase #6 $95.57   6.118%   $101.417   $101.42   $101.40   $101.40  
  Purchase #7 $243.77   12.493%   $274.2242   $274.22   $274.20   $274.20  
  7 purchase totals = $867.05       $953.9704   $953.96   $953.90   $954.00