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 $89.85   12.732%   $101.2897   $101.29   $101.30   $101.30  
  Purchase #2 $184.89   3.397%   $191.1707   $191.17   $191.15   $191.20  
  Purchase #3 $60.48   10.377%   $66.756   $66.76   $66.75   $66.80  
  Purchase #4 $149.85   8.471%   $162.5438   $162.54   $162.55   $162.50  
  Purchase #5 $24.94   10.794%   $27.632   $27.63   $27.65   $27.60  
  Purchase #6 $112.64   10.697%   $124.6891   $124.69   $124.70   $124.70  
  Purchase #7 $203.67   6.785%   $217.489   $217.49   $217.50   $217.50  
  7 purchase totals = $826.32       $891.5703   $891.57   $891.60   $891.60