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 $217.56   9.246%   $237.6756   $237.68   $237.70   $237.70  
  Purchase #2 $88.26   5.589%   $93.1929   $93.19   $93.20   $93.20  
  Purchase #3 $106.45   4.657%   $111.4074   $111.41   $111.40   $111.40  
  Purchase #4 $186.71   11.689%   $208.5345   $208.53   $208.55   $208.50  
  Purchase #5 $88.97   12.502%   $100.093   $100.09   $100.10   $100.10  
  Purchase #6 $52.64   4.416%   $54.9646   $54.96   $54.95   $55.00  
  Purchase #7 $47.61   11.416%   $53.0452   $53.05   $53.05   $53.00  
  7 purchase totals = $788.20       $858.9132   $858.91   $858.95   $858.90