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 $109.93   13.733%   $125.0267   $125.03   $125.05   $125.00  
  Purchase #2 $122.99   7.777%   $132.5549   $132.55   $132.55   $132.60  
  Purchase #3 $8.45   12.150%   $9.4767   $9.48   $9.50   $9.50  
  Purchase #4 $26.97   9.537%   $29.5421   $29.54   $29.55   $29.50  
  Purchase #5 $202.57   6.622%   $215.9842   $215.98   $216.00   $216.00  
  Purchase #6 $247.87   9.409%   $271.1921   $271.19   $271.20   $271.20  
  Purchase #7 $156.63   4.727%   $164.0339   $164.03   $164.05   $164.00  
  7 purchase totals = $875.41       $947.8106   $947.80   $947.90   $947.80