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 $244.71   7.219%   $262.3756   $262.38   $262.40   $262.40  
  Purchase #2 $243.41   9.346%   $266.1591   $266.16   $266.15   $266.20  
  Purchase #3 $26.41   3.787%   $27.4101   $27.41   $27.40   $27.40  
  Purchase #4 $212.73   5.569%   $224.5769   $224.58   $224.60   $224.60  
  Purchase #5 $49.39   5.486%   $52.0995   $52.10   $52.10   $52.10  
  Purchase #6 $146.69   11.678%   $163.8205   $163.82   $163.80   $163.80  
  Purchase #7 $17.90   11.245%   $19.9129   $19.91   $19.90   $19.90  
  7 purchase totals = $941.24       $1,016.3546   $1,016.36   $1,016.35   $1,016.40