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 $57.62   8.610%   $62.5811   $62.58   $62.60   $62.60  
  Purchase #2 $21.76   9.205%   $23.763   $23.76   $23.75   $23.80  
  Purchase #3 $220.98   4.750%   $231.4766   $231.48   $231.50   $231.50  
  Purchase #4 $250.48   6.231%   $266.0874   $266.09   $266.10   $266.10  
  Purchase #5 $170.85   6.547%   $182.0355   $182.04   $182.05   $182.00  
  Purchase #6 $13.29   3.489%   $13.7537   $13.75   $13.75   $13.80  
  Purchase #7 $150.60   5.525%   $158.9207   $158.92   $158.90   $158.90  
  7 purchase totals = $885.58       $938.6180   $938.62   $938.65   $938.70