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	$88.96	13.601%	$101.0594	$101.06	$101.05	$101.10
Purchase #2	$131.85	4.263%	$137.4708	$137.47	$137.45	$137.50
Purchase #3	$96.35	11.411%	$107.3445	$107.34	$107.35	$107.30
Purchase #4	$52.50	7.540%	$56.4585	$56.46	$56.45	$56.50
Purchase #5	$42.44	7.130%	$45.466	$45.47	$45.45	$45.50
Purchase #6	$191.72	5.160%	$201.6128	$201.61	$201.60	$201.60
Purchase #7	$25.42	12.130%	$28.5034	$28.50	$28.50	$28.50
7 purchase totals =	$629.24		$677.9154	$677.91	$677.85	$678.00