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 $242.31   8.126%   $262.0001   $262.00   $262.00   $262.00  
  Purchase #2 $182.72   8.664%   $198.5509   $198.55   $198.55   $198.60  
  Purchase #3 $248.87   7.668%   $267.9534   $267.95   $267.95   $268.00  
  Purchase #4 $218.65   12.499%   $245.9791   $245.98   $246.00   $246.00  
  Purchase #5 $95.63   13.333%   $108.3803   $108.38   $108.40   $108.40  
  Purchase #6 $97.70   12.401%   $109.8158   $109.82   $109.80   $109.80  
  Purchase #7 $72.97   13.651%   $82.9311   $82.93   $82.95   $82.90  
  7 purchase totals = $1,158.85       $1,275.6107   $1,275.61   $1,275.65   $1,275.70