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 $84.27   10.840%   $93.4049   $93.40   $93.40   $93.40  
  Purchase #2 $131.58   6.591%   $140.2524   $140.25   $140.25   $140.30  
  Purchase #3 $219.51   9.844%   $241.1186   $241.12   $241.10   $241.10  
  Purchase #4 $164.28   4.321%   $171.3785   $171.38   $171.40   $171.40  
  Purchase #5 $156.32   12.675%   $176.1336   $176.13   $176.15   $176.10  
  Purchase #6 $141.76   12.631%   $159.6657   $159.67   $159.65   $159.70  
  Purchase #7 $60.70   7.158%   $65.0449   $65.04   $65.05   $65.00  
  7 purchase totals = $958.42       $1,046.9986   $1,046.99   $1,047.00   $1,047.00