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 $214.30   10.149%   $236.0493   $236.05   $236.05   $236.00  
  Purchase #2 $10.84   7.314%   $11.6328   $11.63   $11.65   $11.60  
  Purchase #3 $132.76   13.135%   $150.198   $150.20   $150.20   $150.20  
  Purchase #4 $13.47   13.824%   $15.3321   $15.33   $15.35   $15.30  
  Purchase #5 $58.29   8.591%   $63.2977   $63.30   $63.30   $63.30  
  Purchase #6 $126.47   10.377%   $139.5938   $139.59   $139.60   $139.60  
  Purchase #7 $101.60   5.708%   $107.3993   $107.40   $107.40   $107.40  
  7 purchase totals = $657.73       $723.5030   $723.50   $723.55   $723.40