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 $85.91   9.507%   $94.0775   $94.08   $94.10   $94.10  
  Purchase #2 $122.37   13.599%   $139.0111   $139.01   $139.00   $139.00  
  Purchase #3 $196.90   6.688%   $210.0687   $210.07   $210.05   $210.10  
  Purchase #4 $26.96   13.709%   $30.6559   $30.66   $30.65   $30.70  
  Purchase #5 $111.50   5.114%   $117.2021   $117.20   $117.20   $117.20  
  Purchase #6 $168.69   8.773%   $183.4892   $183.49   $183.50   $183.50  
  Purchase #7 $121.50   13.584%   $138.0046   $138.00   $138.00   $138.00  
  7 purchase totals = $833.83       $912.5091   $912.51   $912.50   $912.60