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 $238.63   6.785%   $254.821   $254.82   $254.80   $254.80  
  Purchase #2 $119.32   7.570%   $128.3525   $128.35   $128.35   $128.40  
  Purchase #3 $236.42   7.853%   $254.9861   $254.99   $255.00   $255.00  
  Purchase #4 $204.92   5.228%   $215.6332   $215.63   $215.65   $215.60  
  Purchase #5 $86.80   6.715%   $92.6286   $92.63   $92.65   $92.60  
  Purchase #6 $58.91   9.659%   $64.6001   $64.60   $64.60   $64.60  
  Purchase #7 $38.62   12.474%   $43.4375   $43.44   $43.45   $43.40  
  7 purchase totals = $983.62       $1,054.4590   $1,054.46   $1,054.50   $1,054.40