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 $175.27   13.151%   $198.3198   $198.32   $198.30   $198.30  
  Purchase #2 $148.29   10.244%   $163.4808   $163.48   $163.50   $163.50  
  Purchase #3 $239.69   9.289%   $261.9548   $261.95   $261.95   $262.00  
  Purchase #4 $122.43   5.748%   $129.4673   $129.47   $129.45   $129.50  
  Purchase #5 $18.72   5.607%   $19.7696   $19.77   $19.75   $19.80  
  Purchase #6 $53.72   5.129%   $56.4753   $56.48   $56.50   $56.50  
  Purchase #7 $196.61   3.118%   $202.7403   $202.74   $202.75   $202.70  
  7 purchase totals = $954.73       $1,032.2079   $1,032.21   $1,032.20   $1,032.30