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	$39.46	7.711%	$42.5028	$42.50	$42.50	$42.50
Purchase #2	$166.51	13.690%	$189.3052	$189.31	$189.30	$189.30
Purchase #3	$177.83	10.596%	$196.6729	$196.67	$196.65	$196.70
Purchase #4	$99.45	13.385%	$112.7614	$112.76	$112.75	$112.80
Purchase #5	$57.81	10.242%	$63.7309	$63.73	$63.75	$63.70
Purchase #6	$101.46	6.734%	$108.2923	$108.29	$108.30	$108.30
Purchase #7	$91.82	10.824%	$101.7586	$101.76	$101.75	$101.80
7 purchase totals =	$734.34		$815.0241	$815.02	$815.00	$815.10