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 $55.95   6.651%   $59.6712   $59.67   $59.65   $59.70  
  Purchase #2 $107.71   10.544%   $119.0669   $119.07   $119.05   $119.10  
  Purchase #3 $97.48   5.642%   $102.9798   $102.98   $103.00   $103.00  
  Purchase #4 $60.43   3.677%   $62.652   $62.65   $62.65   $62.70  
  Purchase #5 $26.55   10.181%   $29.2531   $29.25   $29.25   $29.30  
  Purchase #6 $119.58   12.522%   $134.5538   $134.55   $134.55   $134.60  
  Purchase #7 $17.63   9.490%   $19.3031   $19.30   $19.30   $19.30  
  7 purchase totals = $485.33       $527.4799   $527.47   $527.45   $527.70