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 $214.47   9.461%   $234.761   $234.76   $234.75   $234.80  
  Purchase #2 $236.77   8.391%   $256.6374   $256.64   $256.65   $256.60  
  Purchase #3 $195.95   7.858%   $211.3478   $211.35   $211.35   $211.30  
  Purchase #4 $205.82   5.234%   $216.5926   $216.59   $216.60   $216.60  
  Purchase #5 $90.68   11.764%   $101.3476   $101.35   $101.35   $101.30  
  Purchase #6 $200.26   13.600%   $227.4954   $227.50   $227.50   $227.50  
  Purchase #7 $154.85   5.858%   $163.9211   $163.92   $163.90   $163.90  
  7 purchase totals = $1,298.80       $1,412.1029   $1,412.11   $1,412.10   $1,412.00