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	$37.65	12.720%	$42.4391	$42.44	$42.45	$42.40
Purchase #2	$116.26	9.271%	$127.0385	$127.04	$127.05	$127.00
Purchase #3	$232.61	11.727%	$259.8882	$259.89	$259.90	$259.90
Purchase #4	$250.39	5.369%	$263.8334	$263.83	$263.85	$263.80
Purchase #5	$172.67	7.552%	$185.71	$185.71	$185.70	$185.70
Purchase #6	$26.88	5.852%	$28.453	$28.45	$28.45	$28.50
Purchase #7	$90.47	3.557%	$93.688	$93.69	$93.70	$93.70
7 purchase totals =	$926.93		$1,001.0502	$1,001.05	$1,001.10	$1,001.00