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	$73.56	12.522%	$82.7712	$82.77	$82.75	$82.80
Purchase #2	$76.49	13.212%	$86.5959	$86.60	$86.60	$86.60
Purchase #3	$227.52	13.659%	$258.597	$258.60	$258.60	$258.60
Purchase #4	$55.75	13.668%	$63.3699	$63.37	$63.35	$63.40
Purchase #5	$89.73	7.185%	$96.1771	$96.18	$96.20	$96.20
Purchase #6	$76.39	4.694%	$79.9757	$79.98	$80.00	$80.00
Purchase #7	$216.59	6.108%	$229.8193	$229.82	$229.80	$229.80
7 purchase totals =	$816.03		$897.3061	$897.32	$897.30	$897.40