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 $52.64   6.423%   $56.0211   $56.02   $56.00   $56.00  
  Purchase #2 $249.71   5.361%   $263.097   $263.10   $263.10   $263.10  
  Purchase #3 $98.71   13.803%   $112.3349   $112.33   $112.35   $112.30  
  Purchase #4 $164.56   10.376%   $181.6347   $181.63   $181.65   $181.60  
  Purchase #5 $5.33   11.176%   $5.9257   $5.93   $5.95   $5.90  
  Purchase #6 $57.79   5.619%   $61.0372   $61.04   $61.05   $61.00  
  Purchase #7 $170.90   6.509%   $182.0239   $182.02   $182.00   $182.00  
  7 purchase totals = $799.64       $862.0745   $862.07   $862.10   $861.90