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	$172.42	7.648%	$185.6067	$185.61	$185.60	$185.60
Purchase #2	$152.54	12.474%	$171.5678	$171.57	$171.55	$171.60
Purchase #3	$76.90	13.266%	$87.1016	$87.10	$87.10	$87.10
Purchase #4	$105.65	13.845%	$120.2772	$120.28	$120.30	$120.30
Purchase #5	$29.73	10.702%	$32.9117	$32.91	$32.90	$32.90
Purchase #6	$42.53	12.306%	$47.7637	$47.76	$47.75	$47.80
Purchase #7	$60.95	7.724%	$65.6578	$65.66	$65.65	$65.70
7 purchase totals =	$640.72		$710.8865	$710.89	$710.85	$711.00