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 $70.42   4.213%   $73.3868   $73.39   $73.40   $73.40  
  Purchase #2 $166.62   9.803%   $182.9538   $182.95   $182.95   $183.00  
  Purchase #3 $137.62   13.623%   $156.368   $156.37   $156.35   $156.40  
  Purchase #4 $110.96   7.288%   $119.0468   $119.05   $119.05   $119.00  
  Purchase #5 $77.94   12.394%   $87.5999   $87.60   $87.60   $87.60  
  Purchase #6 $103.28   9.291%   $112.8757   $112.88   $112.90   $112.90  
  Purchase #7 $152.83   5.816%   $161.7186   $161.72   $161.70   $161.70  
  7 purchase totals = $819.67       $893.9496   $893.96   $893.95   $894.00