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 $171.31   8.687%   $186.1917   $186.19   $186.20   $186.20  
  Purchase #2 $44.40   13.853%   $50.5507   $50.55   $50.55   $50.60  
  Purchase #3 $239.75   8.752%   $260.7329   $260.73   $260.75   $260.70  
  Purchase #4 $98.74   4.778%   $103.4578   $103.46   $103.45   $103.50  
  Purchase #5 $127.41   6.609%   $135.8305   $135.83   $135.85   $135.80  
  Purchase #6 $59.85   3.278%   $61.8119   $61.81   $61.80   $61.80  
  Purchase #7 $233.62   7.169%   $250.3682   $250.37   $250.35   $250.40  
  7 purchase totals = $975.08       $1,048.9437   $1,048.94   $1,048.95   $1,049.00