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 $241.81   7.620%   $260.2359   $260.24   $260.25   $260.20  
  Purchase #2 $60.66   10.851%   $67.2422   $67.24   $67.25   $67.20  
  Purchase #3 $86.55   9.302%   $94.6009   $94.60   $94.60   $94.60  
  Purchase #4 $9.81   5.338%   $10.3337   $10.33   $10.35   $10.30  
  Purchase #5 $228.98   9.170%   $249.9775   $249.98   $250.00   $250.00  
  Purchase #6 $67.28   13.438%   $76.3211   $76.32   $76.30   $76.30  
  Purchase #7 $64.54   10.545%   $71.3457   $71.35   $71.35   $71.30  
  7 purchase totals = $759.63       $830.0570   $830.06   $830.10   $829.90