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 $43.44   11.740%   $48.5399   $48.54   $48.55   $48.50  
  Purchase #2 $158.57   9.754%   $174.0369   $174.04   $174.05   $174.00  
  Purchase #3 $106.46   8.327%   $115.3249   $115.32   $115.30   $115.30  
  Purchase #4 $202.53   12.329%   $227.4999   $227.50   $227.50   $227.50  
  Purchase #5 $16.48   9.423%   $18.0329   $18.03   $18.05   $18.00  
  Purchase #6 $87.36   11.799%   $97.6676   $97.67   $97.65   $97.70  
  Purchase #7 $68.94   5.222%   $72.54   $72.54   $72.55   $72.50  
  7 purchase totals = $683.78       $753.6421   $753.64   $753.65   $753.50