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 $34.62   3.533%   $35.8431   $35.84   $35.85   $35.80  
  Purchase #2 $104.55   11.251%   $116.3129   $116.31   $116.30   $116.30  
  Purchase #3 $232.48   11.808%   $259.9312   $259.93   $259.95   $259.90  
  Purchase #4 $94.25   13.105%   $106.6015   $106.60   $106.60   $106.60  
  Purchase #5 $163.88   4.424%   $171.1301   $171.13   $171.15   $171.10  
  Purchase #6 $236.66   4.231%   $246.6731   $246.67   $246.65   $246.70  
  Purchase #7 $24.77   6.235%   $26.3144   $26.31   $26.30   $26.30  
  7 purchase totals = $891.21       $962.8063   $962.79   $962.80   $962.70