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 $82.34   5.210%   $86.6299   $86.63   $86.65   $86.60  
  Purchase #2 $229.80   10.694%   $254.3748   $254.37   $254.35   $254.40  
  Purchase #3 $45.48   4.730%   $47.6312   $47.63   $47.65   $47.60  
  Purchase #4 $185.33   8.776%   $201.5946   $201.59   $201.60   $201.60  
  Purchase #5 $164.93   5.502%   $174.0044   $174.00   $174.00   $174.00  
  Purchase #6 $212.89   13.130%   $240.8425   $240.84   $240.85   $240.80  
  Purchase #7 $230.38   7.611%   $247.9142   $247.91   $247.90   $247.90  
  7 purchase totals = $1,151.15       $1,252.9916   $1,252.97   $1,253.00   $1,252.90