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 $206.57   13.447%   $234.3475   $234.35   $234.35   $234.30  
  Purchase #2 $218.95   7.718%   $235.8486   $235.85   $235.85   $235.80  
  Purchase #3 $16.58   8.106%   $17.924   $17.92   $17.90   $17.90  
  Purchase #4 $16.91   3.856%   $17.562   $17.56   $17.55   $17.60  
  Purchase #5 $229.74   6.419%   $244.487   $244.49   $244.50   $244.50  
  Purchase #6 $233.47   10.717%   $258.491   $258.49   $258.50   $258.50  
  Purchase #7 $155.43   10.839%   $172.2771   $172.28   $172.30   $172.30  
  7 purchase totals = $1,077.65       $1,180.9372   $1,180.94   $1,180.95   $1,180.90