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 $244.70   12.523%   $275.3438   $275.34   $275.35   $275.30  
  Purchase #2 $104.32   12.496%   $117.3558   $117.36   $117.35   $117.40  
  Purchase #3 $122.28   7.741%   $131.7457   $131.75   $131.75   $131.70  
  Purchase #4 $60.81   11.436%   $67.7642   $67.76   $67.75   $67.80  
  Purchase #5 $220.86   5.752%   $233.5639   $233.56   $233.55   $233.60  
  Purchase #6 $143.41   9.577%   $157.1444   $157.14   $157.15   $157.10  
  Purchase #7 $131.33   11.237%   $146.0876   $146.09   $146.10   $146.10  
  7 purchase totals = $1,027.71       $1,129.0054   $1,129.00   $1,129.00   $1,129.00