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 $80.61   6.703%   $86.0133   $86.01   $86.00   $86.00  
  Purchase #2 $23.80   9.370%   $26.0301   $26.03   $26.05   $26.00  
  Purchase #3 $103.31   12.245%   $115.9603   $115.96   $115.95   $116.00  
  Purchase #4 $64.48   3.249%   $66.575   $66.58   $66.60   $66.60  
  Purchase #5 $40.26   9.807%   $44.2083   $44.21   $44.20   $44.20  
  Purchase #6 $162.48   9.233%   $177.4818   $177.48   $177.50   $177.50  
  Purchase #7 $191.32   5.833%   $202.4797   $202.48   $202.50   $202.50  
  7 purchase totals = $666.26       $718.7485   $718.75   $718.80   $718.80