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 $141.48   3.381%   $146.2634   $146.26   $146.25   $146.30  
  Purchase #2 $11.77   3.424%   $12.173   $12.17   $12.15   $12.20  
  Purchase #3 $17.68   5.475%   $18.648   $18.65   $18.65   $18.60  
  Purchase #4 $71.79   4.349%   $74.9121   $74.91   $74.90   $74.90  
  Purchase #5 $155.86   4.164%   $162.35   $162.35   $162.35   $162.40  
  Purchase #6 $192.35   4.619%   $201.2346   $201.23   $201.25   $201.20  
  Purchase #7 $77.61   9.378%   $84.8883   $84.89   $84.90   $84.90  
  7 purchase totals = $668.54       $700.4694   $700.46   $700.45   $700.50