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 $106.97   5.624%   $112.986   $112.99   $113.00   $113.00  
  Purchase #2 $182.38   11.667%   $203.6583   $203.66   $203.65   $203.70  
  Purchase #3 $153.62   10.370%   $169.5504   $169.55   $169.55   $169.60  
  Purchase #4 $97.31   6.116%   $103.2615   $103.26   $103.25   $103.30  
  Purchase #5 $140.34   11.331%   $156.2419   $156.24   $156.25   $156.20  
  Purchase #6 $240.56   9.525%   $263.4733   $263.47   $263.45   $263.50  
  Purchase #7 $27.89   11.691%   $31.1506   $31.15   $31.15   $31.20  
  7 purchase totals = $949.07       $1,040.3220   $1,040.32   $1,040.30   $1,040.50