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	$158.64	7.283%	$170.1938	$170.19	$170.20	$170.20
Purchase #2	$110.28	9.105%	$120.321	$120.32	$120.30	$120.30
Purchase #3	$147.70	13.285%	$167.3219	$167.32	$167.30	$167.30
Purchase #4	$250.94	13.324%	$284.3752	$284.38	$284.40	$284.40
Purchase #5	$59.82	13.437%	$67.858	$67.86	$67.85	$67.90
Purchase #6	$113.73	11.744%	$127.0865	$127.09	$127.10	$127.10
Purchase #7	$208.71	7.122%	$223.5743	$223.57	$223.55	$223.60
7 purchase totals =	$1,049.82		$1,160.7307	$1,160.73	$1,160.70	$1,160.80