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	$250.77	5.393%	$264.294	$264.29	$264.30	$264.30
Purchase #2	$54.32	13.111%	$61.4419	$61.44	$61.45	$61.40
Purchase #3	$36.38	4.560%	$38.0389	$38.04	$38.05	$38.00
Purchase #4	$93.51	6.298%	$99.3993	$99.40	$99.40	$99.40
Purchase #5	$154.38	9.428%	$168.9349	$168.93	$168.95	$168.90
Purchase #6	$160.40	3.561%	$166.1118	$166.11	$166.10	$166.10
Purchase #7	$97.92	10.627%	$108.326	$108.33	$108.35	$108.30
7 purchase totals =	$847.68		$906.5468	$906.54	$906.60	$906.40