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	$166.50	12.529%	$187.3608	$187.36	$187.35	$187.40
Purchase #2	$75.28	11.454%	$83.9026	$83.90	$83.90	$83.90
Purchase #3	$43.32	5.576%	$45.7355	$45.74	$45.75	$45.70
Purchase #4	$124.78	6.727%	$133.174	$133.17	$133.15	$133.20
Purchase #5	$167.44	3.588%	$173.4477	$173.45	$173.45	$173.40
Purchase #6	$237.30	7.813%	$255.8402	$255.84	$255.85	$255.80
Purchase #7	$187.90	6.256%	$199.655	$199.66	$199.65	$199.70
7 purchase totals =	$1,002.52		$1,079.1158	$1,079.12	$1,079.10	$1,079.10