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 $76.40   13.234%   $86.5108   $86.51   $86.50   $86.50  
  Purchase #2 $188.95   10.370%   $208.5441   $208.54   $208.55   $208.50  
  Purchase #3 $29.85   12.522%   $33.5878   $33.59   $33.60   $33.60  
  Purchase #4 $203.29   3.592%   $210.5922   $210.59   $210.60   $210.60  
  Purchase #5 $76.59   5.598%   $80.8775   $80.88   $80.90   $80.90  
  Purchase #6 $202.47   4.830%   $212.2493   $212.25   $212.25   $212.20  
  Purchase #7 $147.70   9.233%   $161.3371   $161.34   $161.35   $161.30  
  7 purchase totals = $925.25       $993.6988   $993.70   $993.75   $993.60