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 $73.42   4.277%   $76.5602   $76.56   $76.55   $76.60  
  Purchase #2 $191.85   12.854%   $216.5104   $216.51   $216.50   $216.50  
  Purchase #3 $198.52   7.789%   $213.9827   $213.98   $214.00   $214.00  
  Purchase #4 $89.90   10.400%   $99.2496   $99.25   $99.25   $99.20  
  Purchase #5 $71.92   7.662%   $77.4305   $77.43   $77.45   $77.40  
  Purchase #6 $185.81   3.830%   $192.9265   $192.93   $192.95   $192.90  
  Purchase #7 $26.55   8.665%   $28.8506   $28.85   $28.85   $28.90  
  7 purchase totals = $837.97       $905.5105   $905.51   $905.55   $905.50