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 $69.95   6.207%   $74.2918   $74.29   $74.30   $74.30  
  Purchase #2 $113.26   10.561%   $125.2214   $125.22   $125.20   $125.20  
  Purchase #3 $159.58   10.825%   $176.8545   $176.85   $176.85   $176.90  
  Purchase #4 $32.62   4.332%   $34.0331   $34.03   $34.05   $34.00  
  Purchase #5 $104.28   5.376%   $109.8861   $109.89   $109.90   $109.90  
  Purchase #6 $236.59   11.380%   $263.5139   $263.51   $263.50   $263.50  
  Purchase #7 $178.30   6.788%   $190.403   $190.40   $190.40   $190.40  
  7 purchase totals = $894.58       $974.2038   $974.19   $974.20   $974.20