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 $47.59   3.664%   $49.3337   $49.33   $49.35   $49.30  
  Purchase #2 $127.43   6.516%   $135.7333   $135.73   $135.75   $135.70  
  Purchase #3 $124.36   10.446%   $137.3506   $137.35   $137.35   $137.40  
  Purchase #4 $196.75   3.417%   $203.4729   $203.47   $203.45   $203.50  
  Purchase #5 $210.91   10.711%   $233.5006   $233.50   $233.50   $233.50  
  Purchase #6 $227.99   11.149%   $253.4086   $253.41   $253.40   $253.40  
  Purchase #7 $61.26   12.523%   $68.9316   $68.93   $68.95   $68.90  
  7 purchase totals = $996.29       $1,081.7313   $1,081.72   $1,081.75   $1,081.70