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 $164.89   13.545%   $187.2244   $187.22   $187.20   $187.20  
  Purchase #2 $217.58   12.268%   $244.2727   $244.27   $244.25   $244.30  
  Purchase #3 $85.45   12.664%   $96.2714   $96.27   $96.25   $96.30  
  Purchase #4 $57.70   10.523%   $63.7718   $63.77   $63.75   $63.80  
  Purchase #5 $76.35   13.177%   $86.4106   $86.41   $86.40   $86.40  
  Purchase #6 $112.35   10.867%   $124.5591   $124.56   $124.55   $124.60  
  Purchase #7 $209.35   7.204%   $224.4316   $224.43   $224.45   $224.40  
  7 purchase totals = $923.67       $1,026.9416   $1,026.93   $1,026.85   $1,027.00