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 $85.58   3.190%   $88.31   $88.31   $88.30   $88.30  
  Purchase #2 $133.46   12.161%   $149.6901   $149.69   $149.70   $149.70  
  Purchase #3 $163.54   8.440%   $177.3428   $177.34   $177.35   $177.30  
  Purchase #4 $86.27   11.204%   $95.9357   $95.94   $95.95   $95.90  
  Purchase #5 $198.47   3.603%   $205.6209   $205.62   $205.60   $205.60  
  Purchase #6 $54.81   3.419%   $56.684   $56.68   $56.70   $56.70  
  Purchase #7 $62.91   4.531%   $65.7605   $65.76   $65.75   $65.80  
  7 purchase totals = $785.04       $839.3440   $839.34   $839.35   $839.30