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 $176.93   12.733%   $199.4585   $199.46   $199.45   $199.50  
  Purchase #2 $227.53   10.261%   $250.8769   $250.88   $250.90   $250.90  
  Purchase #3 $63.39   10.603%   $70.1112   $70.11   $70.10   $70.10  
  Purchase #4 $161.88   11.410%   $180.3505   $180.35   $180.35   $180.40  
  Purchase #5 $96.66   5.187%   $101.6738   $101.67   $101.65   $101.70  
  Purchase #6 $52.50   3.391%   $54.2803   $54.28   $54.30   $54.30  
  Purchase #7 $100.49   5.759%   $106.2772   $106.28   $106.30   $106.30  
  7 purchase totals = $879.38       $963.0284   $963.03   $963.05   $963.20