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 $24.39   6.761%   $26.039   $26.04   $26.05   $26.00  
  Purchase #2 $19.73   5.386%   $20.7927   $20.79   $20.80   $20.80  
  Purchase #3 $244.61   4.309%   $255.1502   $255.15   $255.15   $255.20  
  Purchase #4 $49.29   7.562%   $53.0173   $53.02   $53.00   $53.00  
  Purchase #5 $134.25   5.150%   $141.1639   $141.16   $141.15   $141.20  
  Purchase #6 $59.74   7.445%   $64.1876   $64.19   $64.20   $64.20  
  Purchase #7 $30.99   8.340%   $33.5746   $33.57   $33.55   $33.60  
  7 purchase totals = $563.00       $593.9253   $593.92   $593.90   $594.00