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 $64.59   13.867%   $73.5467   $73.55   $73.55   $73.50  
  Purchase #2 $146.36   10.418%   $161.6078   $161.61   $161.60   $161.60  
  Purchase #3 $66.81   7.809%   $72.0272   $72.03   $72.05   $72.00  
  Purchase #4 $20.88   8.469%   $22.6483   $22.65   $22.65   $22.60  
  Purchase #5 $24.56   6.694%   $26.204   $26.20   $26.20   $26.20  
  Purchase #6 $246.88   10.317%   $272.3506   $272.35   $272.35   $272.40  
  Purchase #7 $196.68   9.528%   $215.4197   $215.42   $215.40   $215.40  
  7 purchase totals = $766.76       $843.8043   $843.81   $843.80   $843.70