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	$242.63	13.476%	$275.3268	$275.33	$275.35	$275.30
Purchase #2	$199.81	5.672%	$211.1432	$211.14	$211.15	$211.10
Purchase #3	$175.40	4.516%	$183.3211	$183.32	$183.30	$183.30
Purchase #4	$95.35	4.760%	$99.8887	$99.89	$99.90	$99.90
Purchase #5	$59.47	13.607%	$67.5621	$67.56	$67.55	$67.60
Purchase #6	$131.66	11.325%	$146.5705	$146.57	$146.55	$146.60
Purchase #7	$81.97	9.870%	$90.0604	$90.06	$90.05	$90.10
7 purchase totals =	$986.29		$1,073.8728	$1,073.87	$1,073.85	$1,073.90