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 $127.83   13.393%   $144.9503   $144.95   $144.95   $145.00  
  Purchase #2 $64.83   7.221%   $69.5114   $69.51   $69.50   $69.50  
  Purchase #3 $64.64   6.758%   $69.0084   $69.01   $69.00   $69.00  
  Purchase #4 $200.35   4.283%   $208.931   $208.93   $208.95   $208.90  
  Purchase #5 $107.79   7.355%   $115.718   $115.72   $115.70   $115.70  
  Purchase #6 $49.42   10.779%   $54.747   $54.75   $54.75   $54.70  
  Purchase #7 $216.44   3.381%   $223.7578   $223.76   $223.75   $223.80  
  7 purchase totals = $831.30       $886.6239   $886.63   $886.60   $886.60