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 $77.93   10.668%   $86.2436   $86.24   $86.25   $86.20  
  Purchase #2 $125.64   9.584%   $137.6813   $137.68   $137.70   $137.70  
  Purchase #3 $70.42   5.654%   $74.4015   $74.40   $74.40   $74.40  
  Purchase #4 $240.65   3.466%   $248.9909   $248.99   $249.00   $249.00  
  Purchase #5 $244.59   7.830%   $263.7414   $263.74   $263.75   $263.70  
  Purchase #6 $60.58   7.471%   $65.1059   $65.11   $65.10   $65.10  
  Purchase #7 $148.28   3.176%   $152.9894   $152.99   $153.00   $153.00  
  7 purchase totals = $968.09       $1,029.1540   $1,029.15   $1,029.20   $1,029.10