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 $244.93   7.220%   $262.6139   $262.61   $262.60   $262.60  
  Purchase #2 $60.92   3.286%   $62.9218   $62.92   $62.90   $62.90  
  Purchase #3 $160.68   13.807%   $182.8651   $182.87   $182.85   $182.90  
  Purchase #4 $144.29   9.618%   $158.1678   $158.17   $158.15   $158.20  
  Purchase #5 $20.89   11.795%   $23.354   $23.35   $23.35   $23.40  
  Purchase #6 $113.38   12.110%   $127.1103   $127.11   $127.10   $127.10  
  Purchase #7 $27.76   4.430%   $28.9898   $28.99   $29.00   $29.00  
  7 purchase totals = $772.85       $846.0227   $846.02   $845.95   $846.10