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	$73.28	13.285%	$83.0152	$83.02	$83.00	$83.00
Purchase #2	$143.46	11.578%	$160.0698	$160.07	$160.05	$160.10
Purchase #3	$117.85	7.501%	$126.6899	$126.69	$126.70	$126.70
Purchase #4	$88.34	3.869%	$91.7579	$91.76	$91.75	$91.80
Purchase #5	$42.99	6.863%	$45.9404	$45.94	$45.95	$45.90
Purchase #6	$177.39	4.449%	$185.2821	$185.28	$185.30	$185.30
Purchase #7	$84.64	6.814%	$90.4074	$90.41	$90.40	$90.40
7 purchase totals =	$727.95		$783.1627	$783.17	$783.15	$783.20