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 $244.95   13.326%   $277.592   $277.59   $277.60   $277.60  
  Purchase #2 $191.93   12.735%   $216.3723   $216.37   $216.35   $216.40  
  Purchase #3 $158.65   11.245%   $176.4902   $176.49   $176.50   $176.50  
  Purchase #4 $46.87   7.857%   $50.5526   $50.55   $50.55   $50.60  
  Purchase #5 $91.99   13.555%   $104.4592   $104.46   $104.45   $104.50  
  Purchase #6 $104.92   10.602%   $116.0436   $116.04   $116.05   $116.00  
  Purchase #7 $247.43   6.518%   $263.5575   $263.56   $263.55   $263.60  
  7 purchase totals = $1,086.74       $1,205.0674   $1,205.06   $1,205.05   $1,205.20