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	$167.79	3.339%	$173.3925	$173.39	$173.40	$173.40
Purchase #2	$167.43	10.680%	$185.3115	$185.31	$185.30	$185.30
Purchase #3	$84.31	10.565%	$93.2174	$93.22	$93.20	$93.20
Purchase #4	$40.81	3.343%	$42.1743	$42.17	$42.15	$42.20
Purchase #5	$103.36	11.823%	$115.5803	$115.58	$115.60	$115.60
Purchase #6	$61.30	11.780%	$68.5211	$68.52	$68.50	$68.50
Purchase #7	$129.89	8.811%	$141.3346	$141.33	$141.35	$141.30
7 purchase totals =	$754.89		$819.5317	$819.52	$819.50	$819.50