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	$43.30	10.126%	$47.6846	$47.68	$47.70	$47.70
Purchase #2	$170.72	8.582%	$185.3712	$185.37	$185.35	$185.40
Purchase #3	$230.48	10.581%	$254.8671	$254.87	$254.85	$254.90
Purchase #4	$53.69	4.724%	$56.2263	$56.23	$56.25	$56.20
Purchase #5	$130.82	6.744%	$139.6425	$139.64	$139.65	$139.60
Purchase #6	$30.62	4.136%	$31.8864	$31.89	$31.90	$31.90
Purchase #7	$31.37	13.761%	$35.6868	$35.69	$35.70	$35.70
7 purchase totals =	$691.00		$751.3649	$751.37	$751.40	$751.40