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 $88.42   5.606%   $93.3768   $93.38   $93.40   $93.40  
  Purchase #2 $241.52   6.659%   $257.6028   $257.60   $257.60   $257.60  
  Purchase #3 $86.89   9.296%   $94.9673   $94.97   $94.95   $95.00  
  Purchase #4 $159.57   13.802%   $181.5939   $181.59   $181.60   $181.60  
  Purchase #5 $57.33   9.560%   $62.8107   $62.81   $62.80   $62.80  
  Purchase #6 $20.87   3.537%   $21.6082   $21.61   $21.60   $21.60  
  Purchase #7 $19.90   7.166%   $21.326   $21.33   $21.35   $21.30  
  7 purchase totals = $674.50       $733.2857   $733.29   $733.30   $733.30