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 $64.54   8.467%   $70.0046   $70.00   $70.00   $70.00  
  Purchase #2 $132.28   7.315%   $141.9563   $141.96   $141.95   $142.00  
  Purchase #3 $99.71   13.391%   $113.0622   $113.06   $113.05   $113.10  
  Purchase #4 $131.62   8.262%   $142.4944   $142.49   $142.50   $142.50  
  Purchase #5 $50.67   11.512%   $56.5031   $56.50   $56.50   $56.50  
  Purchase #6 $131.43   11.813%   $146.9558   $146.96   $146.95   $147.00  
  Purchase #7 $71.70   6.276%   $76.1999   $76.20   $76.20   $76.20  
  7 purchase totals = $681.95       $747.1763   $747.17   $747.15   $747.30