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	$227.75	5.630%	$240.5723	$240.57	$240.55	$240.60
Purchase #2	$85.59	4.428%	$89.3799	$89.38	$89.40	$89.40
Purchase #3	$95.30	8.676%	$103.5682	$103.57	$103.55	$103.60
Purchase #4	$148.88	9.411%	$162.8911	$162.89	$162.90	$162.90
Purchase #5	$56.44	13.852%	$64.2581	$64.26	$64.25	$64.30
Purchase #6	$136.47	7.637%	$146.8922	$146.89	$146.90	$146.90
Purchase #7	$179.45	9.409%	$196.3345	$196.33	$196.35	$196.30
7 purchase totals =	$929.88		$1,003.8963	$1,003.89	$1,003.90	$1,004.00