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	$149.61	12.848%	$168.8319	$168.83	$168.85	$168.80
Purchase #2	$139.39	3.801%	$144.6882	$144.69	$144.70	$144.70
Purchase #3	$48.80	6.831%	$52.1335	$52.13	$52.15	$52.10
Purchase #4	$156.46	6.858%	$167.19	$167.19	$167.20	$167.20
Purchase #5	$136.65	5.585%	$144.2819	$144.28	$144.30	$144.30
Purchase #6	$79.27	9.306%	$86.6469	$86.65	$86.65	$86.60
Purchase #7	$97.36	12.775%	$109.7977	$109.80	$109.80	$109.80
7 purchase totals =	$807.54		$873.5701	$873.57	$873.65	$873.50