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 $58.77   9.398%   $64.2932   $64.29   $64.30   $64.30  
  Purchase #2 $112.45   9.684%   $123.3397   $123.34   $123.35   $123.30  
  Purchase #3 $227.38   9.125%   $248.1284   $248.13   $248.15   $248.10  
  Purchase #4 $91.37   5.419%   $96.3213   $96.32   $96.30   $96.30  
  Purchase #5 $212.66   8.481%   $230.6957   $230.70   $230.70   $230.70  
  Purchase #6 $164.65   6.559%   $175.4494   $175.45   $175.45   $175.40  
  Purchase #7 $89.63   4.772%   $93.9071   $93.91   $93.90   $93.90  
  7 purchase totals = $956.91       $1,032.1348   $1,032.14   $1,032.15   $1,032.00