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 $113.77   11.184%   $126.494   $126.49   $126.50   $126.50  
  Purchase #2 $148.83   5.250%   $156.6436   $156.64   $156.65   $156.60  
  Purchase #3 $111.69   6.760%   $119.2402   $119.24   $119.25   $119.20  
  Purchase #4 $119.48   11.217%   $132.8821   $132.88   $132.90   $132.90  
  Purchase #5 $199.58   11.422%   $222.376   $222.38   $222.40   $222.40  
  Purchase #6 $135.93   8.532%   $147.5275   $147.53   $147.55   $147.50  
  Purchase #7 $126.58   6.862%   $135.2659   $135.27   $135.25   $135.30  
  7 purchase totals = $955.86       $1,040.4293   $1,040.43   $1,040.50   $1,040.40