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 $86.44   8.728%   $93.9845   $93.98   $94.00   $94.00  
  Purchase #2 $58.95   13.418%   $66.8599   $66.86   $66.85   $66.90  
  Purchase #3 $175.89   5.805%   $186.1004   $186.10   $186.10   $186.10  
  Purchase #4 $48.95   5.461%   $51.6232   $51.62   $51.60   $51.60  
  Purchase #5 $99.84   6.672%   $106.5013   $106.50   $106.50   $106.50  
  Purchase #6 $132.41   3.175%   $136.614   $136.61   $136.60   $136.60  
  Purchase #7 $31.36   9.418%   $34.3135   $34.31   $34.30   $34.30  
  7 purchase totals = $633.84       $675.9968   $675.98   $675.95   $676.00