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 $250.70   5.578%   $264.684   $264.68   $264.70   $264.70  
  Purchase #2 $229.72   11.398%   $255.9035   $255.90   $255.90   $255.90  
  Purchase #3 $211.81   7.598%   $227.9033   $227.90   $227.90   $227.90  
  Purchase #4 $167.80   7.725%   $180.7626   $180.76   $180.75   $180.80  
  Purchase #5 $186.49   3.297%   $192.6386   $192.64   $192.65   $192.60  
  Purchase #6 $98.77   11.361%   $109.9913   $109.99   $110.00   $110.00  
  Purchase #7 $130.56   8.792%   $142.0388   $142.04   $142.05   $142.00  
  7 purchase totals = $1,275.85       $1,373.9221   $1,373.91   $1,373.95   $1,373.90