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 $186.52   8.267%   $201.9396   $201.94   $201.95   $201.90  
  Purchase #2 $85.86   12.658%   $96.7282   $96.73   $96.75   $96.70  
  Purchase #3 $232.54   7.149%   $249.1643   $249.16   $249.15   $249.20  
  Purchase #4 $199.85   4.114%   $208.0718   $208.07   $208.05   $208.10  
  Purchase #5 $123.43   6.587%   $131.5603   $131.56   $131.55   $131.60  
  Purchase #6 $220.30   3.430%   $227.8563   $227.86   $227.85   $227.90  
  Purchase #7 $120.39   11.400%   $134.1145   $134.11   $134.10   $134.10  
  7 purchase totals = $1,168.89       $1,249.4350   $1,249.43   $1,249.40   $1,249.50