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 $48.68   12.841%   $54.931   $54.93   $54.95   $54.90  
  Purchase #2 $176.93   9.344%   $193.4623   $193.46   $193.45   $193.50  
  Purchase #3 $211.63   8.863%   $230.3868   $230.39   $230.40   $230.40  
  Purchase #4 $98.75   11.338%   $109.9463   $109.95   $109.95   $109.90  
  Purchase #5 $178.54   6.736%   $190.5665   $190.57   $190.55   $190.60  
  Purchase #6 $101.40   5.823%   $107.3045   $107.30   $107.30   $107.30  
  Purchase #7 $177.25   5.579%   $187.1388   $187.14   $187.15   $187.10  
  7 purchase totals = $993.18       $1,073.7362   $1,073.74   $1,073.75   $1,073.70