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	$37.42	6.550%	$39.871	$39.87	$39.85	$39.90
Purchase #2	$83.86	10.467%	$92.6376	$92.64	$92.65	$92.60
Purchase #3	$37.55	7.335%	$40.3043	$40.30	$40.30	$40.30
Purchase #4	$146.76	4.590%	$153.4963	$153.50	$153.50	$153.50
Purchase #5	$58.61	5.151%	$61.629	$61.63	$61.65	$61.60
Purchase #6	$175.27	9.171%	$191.344	$191.34	$191.35	$191.30
Purchase #7	$205.56	6.285%	$218.4794	$218.48	$218.50	$218.50
7 purchase totals =	$745.03		$797.7616	$797.76	$797.80	$797.70