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 $86.73   10.145%   $95.5288   $95.53   $95.55   $95.50  
  Purchase #2 $153.65   4.342%   $160.3215   $160.32   $160.30   $160.30  
  Purchase #3 $128.70   8.838%   $140.0745   $140.07   $140.05   $140.10  
  Purchase #4 $183.84   5.165%   $193.3353   $193.34   $193.35   $193.30  
  Purchase #5 $193.81   13.517%   $220.0073   $220.01   $220.00   $220.00  
  Purchase #6 $35.77   8.592%   $38.8434   $38.84   $38.85   $38.80  
  Purchase #7 $86.75   9.822%   $95.2706   $95.27   $95.25   $95.30  
  7 purchase totals = $869.25       $943.3814   $943.38   $943.35   $943.30