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 $224.65   7.362%   $241.1887   $241.19   $241.20   $241.20  
  Purchase #2 $25.71   5.142%   $27.032   $27.03   $27.05   $27.00  
  Purchase #3 $119.34   4.509%   $124.721   $124.72   $124.70   $124.70  
  Purchase #4 $198.55   12.304%   $222.9796   $222.98   $223.00   $223.00  
  Purchase #5 $238.98   11.433%   $266.3026   $266.30   $266.30   $266.30  
  Purchase #6 $174.99   3.643%   $181.3649   $181.36   $181.35   $181.40  
  Purchase #7 $227.74   4.469%   $237.9177   $237.92   $237.90   $237.90  
  7 purchase totals = $1,209.96       $1,301.5065   $1,301.50   $1,301.50   $1,301.50