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	$106.56	13.483%	$120.9275	$120.93	$120.95	$120.90
Purchase #2	$243.85	6.387%	$259.4247	$259.42	$259.40	$259.40
Purchase #3	$105.41	3.279%	$108.8664	$108.87	$108.85	$108.90
Purchase #4	$127.85	5.422%	$134.782	$134.78	$134.80	$134.80
Purchase #5	$154.78	3.464%	$160.1416	$160.14	$160.15	$160.10
Purchase #6	$31.46	6.485%	$33.5002	$33.50	$33.50	$33.50
Purchase #7	$140.49	12.594%	$158.1833	$158.18	$158.20	$158.20
7 purchase totals =	$910.40		$975.8257	$975.82	$975.85	$975.80