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 $32.48   11.668%   $36.2698   $36.27   $36.25   $36.30  
  Purchase #2 $37.56   12.394%   $42.2152   $42.22   $42.20   $42.20  
  Purchase #3 $5.60   6.805%   $5.9811   $5.98   $6.00   $6.00  
  Purchase #4 $250.65   6.657%   $267.3358   $267.34   $267.35   $267.30  
  Purchase #5 $88.41   11.312%   $98.4109   $98.41   $98.40   $98.40  
  Purchase #6 $216.71   4.541%   $226.5508   $226.55   $226.55   $226.60  
  Purchase #7 $118.71   13.452%   $134.6789   $134.68   $134.70   $134.70  
  7 purchase totals = $750.12       $811.4425   $811.45   $811.45   $811.50