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 $23.52   3.133%   $24.2569   $24.26   $24.25   $24.30  
  Purchase #2 $112.70   10.202%   $124.1977   $124.20   $124.20   $124.20  
  Purchase #3 $223.76   8.162%   $242.0233   $242.02   $242.00   $242.00  
  Purchase #4 $94.69   12.317%   $106.353   $106.35   $106.35   $106.40  
  Purchase #5 $224.85   7.545%   $241.8149   $241.81   $241.80   $241.80  
  Purchase #6 $68.71   12.252%   $77.1283   $77.13   $77.15   $77.10  
  Purchase #7 $6.84   3.730%   $7.0951   $7.10   $7.10   $7.10  
  7 purchase totals = $755.07       $822.8692   $822.87   $822.85   $822.90