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 $24.86   4.320%   $25.934   $25.93   $25.95   $25.90  
  Purchase #2 $44.39   4.417%   $46.3507   $46.35   $46.35   $46.40  
  Purchase #3 $149.87   7.747%   $161.4804   $161.48   $161.50   $161.50  
  Purchase #4 $241.81   12.666%   $272.4377   $272.44   $272.45   $272.40  
  Purchase #5 $165.51   4.858%   $173.5505   $173.55   $173.55   $173.60  
  Purchase #6 $119.35   13.238%   $135.1496   $135.15   $135.15   $135.10  
  Purchase #7 $49.89   11.630%   $55.6922   $55.69   $55.70   $55.70  
  7 purchase totals = $795.68       $870.5951   $870.59   $870.65   $870.60