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	$219.50	13.736%	$249.6505	$249.65	$249.65	$249.70
Purchase #2	$53.61	5.463%	$56.5387	$56.54	$56.55	$56.50
Purchase #3	$139.75	13.658%	$158.8371	$158.84	$158.85	$158.80
Purchase #4	$93.37	7.737%	$100.594	$100.59	$100.60	$100.60
Purchase #5	$143.91	9.110%	$157.0202	$157.02	$157.00	$157.00
Purchase #6	$136.68	9.599%	$149.7999	$149.80	$149.80	$149.80
Purchase #7	$96.40	13.549%	$109.4612	$109.46	$109.45	$109.50
7 purchase totals =	$883.22		$981.9016	$981.90	$981.90	$981.90