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 $231.64   9.629%   $253.9446   $253.94   $253.95   $253.90  
  Purchase #2 $208.43   12.824%   $235.1591   $235.16   $235.15   $235.20  
  Purchase #3 $153.84   8.626%   $167.1102   $167.11   $167.10   $167.10  
  Purchase #4 $60.99   6.528%   $64.9714   $64.97   $64.95   $65.00  
  Purchase #5 $18.98   11.273%   $21.1196   $21.12   $21.10   $21.10  
  Purchase #6 $28.78   6.440%   $30.6334   $30.63   $30.65   $30.60  
  Purchase #7 $238.40   4.385%   $248.8538   $248.85   $248.85   $248.90  
  7 purchase totals = $941.06       $1,021.7921   $1,021.78   $1,021.75   $1,021.80