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 $250.36   6.705%   $267.1466   $267.15   $267.15   $267.10  
  Purchase #2 $33.28   7.747%   $35.8582   $35.86   $35.85   $35.90  
  Purchase #3 $36.26   13.567%   $41.1794   $41.18   $41.20   $41.20  
  Purchase #4 $213.47   11.439%   $237.8888   $237.89   $237.90   $237.90  
  Purchase #5 $111.51   11.368%   $124.1865   $124.19   $124.20   $124.20  
  Purchase #6 $215.37   12.338%   $241.9424   $241.94   $241.95   $241.90  
  Purchase #7 $188.69   8.321%   $204.3909   $204.39   $204.40   $204.40  
  7 purchase totals = $1,048.94       $1,152.5928   $1,152.60   $1,152.65   $1,152.60