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 $36.35   13.624%   $41.3023   $41.30   $41.30   $41.30  
  Purchase #2 $235.77   12.491%   $265.22   $265.22   $265.20   $265.20  
  Purchase #3 $77.98   6.193%   $82.8093   $82.81   $82.80   $82.80  
  Purchase #4 $116.32   8.485%   $126.1898   $126.19   $126.20   $126.20  
  Purchase #5 $103.58   3.659%   $107.37   $107.37   $107.35   $107.40  
  Purchase #6 $83.33   5.248%   $87.7032   $87.70   $87.70   $87.70  
  Purchase #7 $96.75   11.257%   $107.6411   $107.64   $107.65   $107.60  
  7 purchase totals = $750.08       $818.2357   $818.23   $818.20   $818.20