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 $63.66   12.802%   $71.8098   $71.81   $71.80   $71.80  
  Purchase #2 $116.75   4.787%   $122.3388   $122.34   $122.35   $122.30  
  Purchase #3 $84.72   9.285%   $92.5863   $92.59   $92.60   $92.60  
  Purchase #4 $126.78   11.845%   $141.7971   $141.80   $141.80   $141.80  
  Purchase #5 $162.50   13.536%   $184.496   $184.50   $184.50   $184.50  
  Purchase #6 $139.71   6.798%   $149.2075   $149.21   $149.20   $149.20  
  Purchase #7 $9.29   5.404%   $9.792   $9.79   $9.80   $9.80  
  7 purchase totals = $703.41       $772.0275   $772.04   $772.05   $772.00