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 $234.37   7.484%   $251.9103   $251.91   $251.90   $251.90  
  Purchase #2 $199.57   5.838%   $211.2209   $211.22   $211.20   $211.20  
  Purchase #3 $69.81   5.357%   $73.5497   $73.55   $73.55   $73.50  
  Purchase #4 $231.69   5.680%   $244.85   $244.85   $244.85   $244.90  
  Purchase #5 $16.55   9.239%   $18.0791   $18.08   $18.10   $18.10  
  Purchase #6 $71.41   6.682%   $76.1816   $76.18   $76.20   $76.20  
  Purchase #7 $81.87   7.738%   $88.2051   $88.21   $88.20   $88.20  
  7 purchase totals = $905.27       $963.9967   $964.00   $964.00   $964.00