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 $239.93   10.633%   $265.4418   $265.44   $265.45   $265.40  
  Purchase #2 $20.88   8.245%   $22.6016   $22.60   $22.60   $22.60  
  Purchase #3 $212.89   4.572%   $222.6233   $222.62   $222.60   $222.60  
  Purchase #4 $199.49   11.774%   $222.978   $222.98   $223.00   $223.00  
  Purchase #5 $53.45   9.160%   $58.346   $58.35   $58.35   $58.30  
  Purchase #6 $187.71   9.874%   $206.2445   $206.24   $206.25   $206.20  
  Purchase #7 $206.37   5.333%   $217.3757   $217.38   $217.40   $217.40  
  7 purchase totals = $1,120.72       $1,215.6109   $1,215.61   $1,215.65   $1,215.50