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	$93.76	6.376%	$99.7381	$99.74	$99.75	$99.70
Purchase #2	$222.30	13.198%	$251.6392	$251.64	$251.65	$251.60
Purchase #3	$211.93	10.701%	$234.6086	$234.61	$234.60	$234.60
Purchase #4	$111.82	10.281%	$123.3162	$123.32	$123.30	$123.30
Purchase #5	$250.89	4.619%	$262.4786	$262.48	$262.50	$262.50
Purchase #6	$219.89	13.303%	$249.142	$249.14	$249.15	$249.10
Purchase #7	$168.77	12.250%	$189.4443	$189.44	$189.45	$189.40
7 purchase totals =	$1,279.36		$1,410.3670	$1,410.37	$1,410.40	$1,410.20