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 $24.39   6.623%   $26.0053   $26.01   $26.00   $26.00  
  Purchase #2 $63.31   5.825%   $66.9978   $67.00   $67.00   $67.00  
  Purchase #3 $79.79   4.642%   $83.4939   $83.49   $83.50   $83.50  
  Purchase #4 $188.33   5.248%   $198.2136   $198.21   $198.20   $198.20  
  Purchase #5 $93.35   10.785%   $103.4178   $103.42   $103.40   $103.40  
  Purchase #6 $208.91   11.239%   $232.3894   $232.39   $232.40   $232.40  
  Purchase #7 $191.88   3.401%   $198.4058   $198.41   $198.40   $198.40  
  7 purchase totals = $849.96       $908.9236   $908.93   $908.90   $908.90