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	$71.84	9.791%	$78.8739	$78.87	$78.85	$78.90
Purchase #2	$194.42	11.848%	$217.4549	$217.45	$217.45	$217.50
Purchase #3	$157.28	11.135%	$174.7931	$174.79	$174.80	$174.80
Purchase #4	$65.49	10.118%	$72.1163	$72.12	$72.10	$72.10
Purchase #5	$5.98	4.364%	$6.241	$6.24	$6.25	$6.20
Purchase #6	$81.56	10.154%	$89.8416	$89.84	$89.85	$89.80
Purchase #7	$220.27	10.835%	$244.1363	$244.14	$244.15	$244.10
7 purchase totals =	$796.84		$883.4571	$883.45	$883.45	$883.40