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	$201.77	10.826%	$223.6136	$223.61	$223.60	$223.60
Purchase #2	$115.27	7.814%	$124.2772	$124.28	$124.30	$124.30
Purchase #3	$248.82	5.218%	$261.8034	$261.80	$261.80	$261.80
Purchase #4	$97.80	8.294%	$105.9115	$105.91	$105.90	$105.90
Purchase #5	$25.32	7.180%	$27.138	$27.14	$27.15	$27.10
Purchase #6	$96.37	13.782%	$109.6517	$109.65	$109.65	$109.70
Purchase #7	$121.86	4.863%	$127.7861	$127.79	$127.80	$127.80
7 purchase totals =	$907.21		$980.1815	$980.18	$980.20	$980.20