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 $90.63   6.590%   $96.6025   $96.60   $96.60   $96.60  
  Purchase #2 $225.87   6.778%   $241.1795   $241.18   $241.20   $241.20  
  Purchase #3 $52.90   3.586%   $54.797   $54.80   $54.80   $54.80  
  Purchase #4 $224.59   9.387%   $245.6723   $245.67   $245.65   $245.70  
  Purchase #5 $148.82   10.849%   $164.9655   $164.97   $164.95   $165.00  
  Purchase #6 $224.71   12.389%   $252.5493   $252.55   $252.55   $252.50  
  Purchase #7 $186.90   5.638%   $197.4374   $197.44   $197.45   $197.40  
  7 purchase totals = $1,154.42       $1,253.2035   $1,253.21   $1,253.20   $1,253.20