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	$135.48	12.272%	$152.1061	$152.11	$152.10	$152.10
Purchase #2	$59.40	5.649%	$62.7555	$62.76	$62.75	$62.80
Purchase #3	$238.27	4.300%	$248.5156	$248.52	$248.50	$248.50
Purchase #4	$108.57	5.412%	$114.4458	$114.45	$114.45	$114.40
Purchase #5	$39.85	5.450%	$42.0218	$42.02	$42.00	$42.00
Purchase #6	$102.39	6.398%	$108.9409	$108.94	$108.95	$108.90
Purchase #7	$161.74	6.529%	$172.3	$172.30	$172.30	$172.30
7 purchase totals =	$845.70		$901.0857	$901.10	$901.05	$901.00