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 $38.77   5.874%   $41.0473   $41.05   $41.05   $41.00  
  Purchase #2 $80.28   5.560%   $84.7436   $84.74   $84.75   $84.70  
  Purchase #3 $26.35   3.206%   $27.1948   $27.19   $27.20   $27.20  
  Purchase #4 $50.46   13.672%   $57.3589   $57.36   $57.35   $57.40  
  Purchase #5 $189.49   13.176%   $214.4572   $214.46   $214.45   $214.50  
  Purchase #6 $235.83   8.353%   $255.5289   $255.53   $255.55   $255.50  
  Purchase #7 $81.93   4.533%   $85.6439   $85.64   $85.65   $85.60  
  7 purchase totals = $703.11       $765.9746   $765.97   $766.00   $765.90