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 $58.66   4.583%   $61.3484   $61.35   $61.35   $61.30  
  Purchase #2 $119.51   11.163%   $132.8509   $132.85   $132.85   $132.90  
  Purchase #3 $30.53   9.155%   $33.325   $33.33   $33.35   $33.30  
  Purchase #4 $188.50   13.608%   $214.1511   $214.15   $214.15   $214.20  
  Purchase #5 $249.61   5.212%   $262.6197   $262.62   $262.60   $262.60  
  Purchase #6 $103.87   8.210%   $112.3977   $112.40   $112.40   $112.40  
  Purchase #7 $147.93   10.848%   $163.9774   $163.98   $164.00   $164.00  
  7 purchase totals = $898.61       $980.6702   $980.68   $980.70   $980.70