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 $202.53   12.110%   $227.0564   $227.06   $227.05   $227.10  
  Purchase #2 $11.36   12.239%   $12.7504   $12.75   $12.75   $12.80  
  Purchase #3 $127.27   4.374%   $132.8368   $132.84   $132.85   $132.80  
  Purchase #4 $230.43   12.685%   $259.66   $259.66   $259.65   $259.70  
  Purchase #5 $46.88   5.110%   $49.2756   $49.28   $49.30   $49.30  
  Purchase #6 $174.28   4.717%   $182.5008   $182.50   $182.50   $182.50  
  Purchase #7 $126.40   11.482%   $140.9132   $140.91   $140.90   $140.90  
  7 purchase totals = $919.15       $1,004.9932   $1,005.00   $1,005.00   $1,005.10