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 $78.57   6.801%   $83.9135   $83.91   $83.90   $83.90  
  Purchase #2 $22.49   5.278%   $23.677   $23.68   $23.70   $23.70  
  Purchase #3 $195.42   4.235%   $203.696   $203.70   $203.70   $203.70  
  Purchase #4 $48.69   13.448%   $55.2378   $55.24   $55.25   $55.20  
  Purchase #5 $228.34   13.706%   $259.6363   $259.64   $259.65   $259.60  
  Purchase #6 $149.88   12.106%   $168.0245   $168.02   $168.00   $168.00  
  Purchase #7 $204.71   7.792%   $220.661   $220.66   $220.65   $220.70  
  7 purchase totals = $928.10       $1,014.8461   $1,014.85   $1,014.85   $1,014.80