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 $8.28   8.311%   $8.9682   $8.97   $8.95   $9.00  
  Purchase #2 $130.96   8.601%   $142.2239   $142.22   $142.20   $142.20  
  Purchase #3 $175.83   9.126%   $191.8762   $191.88   $191.90   $191.90  
  Purchase #4 $11.36   13.177%   $12.8569   $12.86   $12.85   $12.90  
  Purchase #5 $150.54   10.664%   $166.5936   $166.59   $166.60   $166.60  
  Purchase #6 $128.79   13.438%   $146.0968   $146.10   $146.10   $146.10  
  Purchase #7 $76.88   5.209%   $80.8847   $80.88   $80.90   $80.90  
  7 purchase totals = $682.64       $749.5003   $749.50   $749.50   $749.60