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 $227.73   6.578%   $242.7101   $242.71   $242.70   $242.70  
  Purchase #2 $248.93   7.139%   $266.7011   $266.70   $266.70   $266.70  
  Purchase #3 $119.50   11.214%   $132.9007   $132.90   $132.90   $132.90  
  Purchase #4 $125.78   4.551%   $131.5042   $131.50   $131.50   $131.50  
  Purchase #5 $7.37   13.758%   $8.384   $8.38   $8.40   $8.40  
  Purchase #6 $41.34   13.536%   $46.9358   $46.94   $46.95   $46.90  
  Purchase #7 $59.64   13.686%   $67.8023   $67.80   $67.80   $67.80  
  7 purchase totals = $830.29       $896.9382   $896.93   $896.95   $896.90