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 $200.48   12.726%   $225.9931   $225.99   $226.00   $226.00  
  Purchase #2 $48.40   10.598%   $53.5294   $53.53   $53.55   $53.50  
  Purchase #3 $76.92   6.764%   $82.1229   $82.12   $82.10   $82.10  
  Purchase #4 $98.70   8.114%   $106.7085   $106.71   $106.70   $106.70  
  Purchase #5 $212.47   5.655%   $224.4852   $224.49   $224.50   $224.50  
  Purchase #6 $172.25   11.110%   $191.387   $191.39   $191.40   $191.40  
  Purchase #7 $19.25   8.290%   $20.8458   $20.85   $20.85   $20.80  
  7 purchase totals = $828.47       $905.0719   $905.08   $905.10   $905.00