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 $54.76   9.215%   $59.8061   $59.81   $59.80   $59.80  
  Purchase #2 $50.27   12.598%   $56.603   $56.60   $56.60   $56.60  
  Purchase #3 $77.47   12.789%   $87.3776   $87.38   $87.40   $87.40  
  Purchase #4 $159.52   5.436%   $168.1915   $168.19   $168.20   $168.20  
  Purchase #5 $237.48   9.464%   $259.9551   $259.96   $259.95   $260.00  
  Purchase #6 $143.29   6.799%   $153.0323   $153.03   $153.05   $153.00  
  Purchase #7 $161.97   6.351%   $172.2567   $172.26   $172.25   $172.30  
  7 purchase totals = $884.76       $957.2223   $957.23   $957.25   $957.30