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	$140.32	4.308%	$146.365	$146.37	$146.35	$146.40
Purchase #2	$205.63	6.194%	$218.3667	$218.37	$218.35	$218.40
Purchase #3	$119.58	12.608%	$134.6566	$134.66	$134.65	$134.70
Purchase #4	$11.33	10.655%	$12.5372	$12.54	$12.55	$12.50
Purchase #5	$80.56	3.244%	$83.1734	$83.17	$83.15	$83.20
Purchase #6	$245.41	9.303%	$268.2405	$268.24	$268.25	$268.20
Purchase #7	$123.67	3.129%	$127.5396	$127.54	$127.55	$127.50
7 purchase totals =	$926.50		$990.8790	$990.89	$990.85	$990.90