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	$99.84	3.428%	$103.2625	$103.26	$103.25	$103.30
Purchase #2	$250.65	9.530%	$274.5369	$274.54	$274.55	$274.50
Purchase #3	$147.58	7.181%	$158.1777	$158.18	$158.20	$158.20
Purchase #4	$123.47	11.339%	$137.4703	$137.47	$137.45	$137.50
Purchase #5	$177.60	5.562%	$187.4781	$187.48	$187.50	$187.50
Purchase #6	$7.33	6.477%	$7.8048	$7.80	$7.80	$7.80
Purchase #7	$139.92	8.549%	$151.8818	$151.88	$151.90	$151.90
7 purchase totals =	$946.39		$1,020.6121	$1,020.61	$1,020.65	$1,020.70