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	$160.43	6.376%	$170.659	$170.66	$170.65	$170.70
Purchase #2	$141.68	5.105%	$148.9128	$148.91	$148.90	$148.90
Purchase #3	$139.83	5.430%	$147.4228	$147.42	$147.40	$147.40
Purchase #4	$145.89	11.572%	$162.7724	$162.77	$162.75	$162.80
Purchase #5	$110.88	11.500%	$123.6312	$123.63	$123.65	$123.60
Purchase #6	$166.57	7.144%	$178.4698	$178.47	$178.45	$178.50
Purchase #7	$228.41	8.355%	$247.4937	$247.49	$247.50	$247.50
7 purchase totals =	$1,093.69		$1,179.3617	$1,179.35	$1,179.30	$1,179.40