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	$62.70	13.340%	$71.0642	$71.06	$71.05	$71.10
Purchase #2	$149.69	4.110%	$155.8423	$155.84	$155.85	$155.80
Purchase #3	$62.45	12.593%	$70.3143	$70.31	$70.30	$70.30
Purchase #4	$131.51	4.730%	$137.7304	$137.73	$137.75	$137.70
Purchase #5	$205.66	8.656%	$223.4619	$223.46	$223.45	$223.50
Purchase #6	$85.59	6.531%	$91.1799	$91.18	$91.20	$91.20
Purchase #7	$224.92	12.545%	$253.1362	$253.14	$253.15	$253.10
7 purchase totals =	$922.52		$1,002.7292	$1,002.72	$1,002.75	$1,002.70