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 $72.67   7.277%   $77.9582   $77.96   $77.95   $78.00  
  Purchase #2 $141.70   3.365%   $146.4682   $146.47   $146.45   $146.50  
  Purchase #3 $15.41   7.170%   $16.5149   $16.51   $16.50   $16.50  
  Purchase #4 $166.80   7.409%   $179.1582   $179.16   $179.15   $179.20  
  Purchase #5 $46.83   8.131%   $50.6377   $50.64   $50.65   $50.60  
  Purchase #6 $203.45   4.165%   $211.9237   $211.92   $211.90   $211.90  
  Purchase #7 $54.58   6.214%   $57.9716   $57.97   $57.95   $58.00  
  7 purchase totals = $701.44       $740.6325   $740.63   $740.55   $740.70