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 $53.60   11.132%   $59.5668   $59.57   $59.55   $59.60  
  Purchase #2 $93.46   5.559%   $98.6554   $98.66   $98.65   $98.70  
  Purchase #3 $23.78   13.490%   $26.9879   $26.99   $27.00   $27.00  
  Purchase #4 $166.93   9.606%   $182.9653   $182.97   $182.95   $183.00  
  Purchase #5 $248.97   12.831%   $280.9153   $280.92   $280.90   $280.90  
  Purchase #6 $166.49   11.542%   $185.7063   $185.71   $185.70   $185.70  
  Purchase #7 $101.37   7.576%   $109.0498   $109.05   $109.05   $109.00  
  7 purchase totals = $854.60       $943.8468   $943.87   $943.80   $943.90