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	$209.55	9.358%	$229.1597	$229.16	$229.15	$229.20
Purchase #2	$95.55	10.479%	$105.5627	$105.56	$105.55	$105.60
Purchase #3	$206.95	6.568%	$220.5425	$220.54	$220.55	$220.50
Purchase #4	$57.34	9.334%	$62.6921	$62.69	$62.70	$62.70
Purchase #5	$84.60	6.528%	$90.1227	$90.12	$90.10	$90.10
Purchase #6	$145.43	10.809%	$161.1495	$161.15	$161.15	$161.10
Purchase #7	$65.64	9.140%	$71.6395	$71.64	$71.65	$71.60
7 purchase totals =	$865.06		$940.8687	$940.86	$940.85	$940.80