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 $75.96   13.574%   $86.2708   $86.27   $86.25   $86.30  
  Purchase #2 $187.66   5.704%   $198.3641   $198.36   $198.35   $198.40  
  Purchase #3 $185.27   11.706%   $206.9577   $206.96   $206.95   $207.00  
  Purchase #4 $203.93   6.853%   $217.9053   $217.91   $217.90   $217.90  
  Purchase #5 $158.74   4.605%   $166.05   $166.05   $166.05   $166.10  
  Purchase #6 $5.97   6.427%   $6.3537   $6.35   $6.35   $6.40  
  Purchase #7 $8.49   6.461%   $9.0385   $9.04   $9.05   $9.00  
  7 purchase totals = $826.02       $890.9401   $890.94   $890.90   $891.10