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 $83.32   12.682%   $93.8866   $93.89   $93.90   $93.90  
  Purchase #2 $191.81   10.355%   $211.6719   $211.67   $211.65   $211.70  
  Purchase #3 $77.67   6.782%   $82.9376   $82.94   $82.95   $82.90  
  Purchase #4 $223.86   4.428%   $233.7725   $233.77   $233.75   $233.80  
  Purchase #5 $237.88   11.678%   $265.6596   $265.66   $265.65   $265.70  
  Purchase #6 $204.87   5.130%   $215.3798   $215.38   $215.40   $215.40  
  Purchase #7 $54.60   6.714%   $58.2658   $58.27   $58.25   $58.30  
  7 purchase totals = $1,074.01       $1,161.5738   $1,161.58   $1,161.55   $1,161.70