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	$65.72	8.182%	$71.0972	$71.10	$71.10	$71.10
Purchase #2	$58.73	5.847%	$62.1639	$62.16	$62.15	$62.20
Purchase #3	$50.30	6.294%	$53.4659	$53.47	$53.45	$53.50
Purchase #4	$192.68	8.553%	$209.1599	$209.16	$209.15	$209.20
Purchase #5	$23.79	7.729%	$25.6287	$25.63	$25.65	$25.60
Purchase #6	$68.56	4.108%	$71.3764	$71.38	$71.40	$71.40
Purchase #7	$79.27	11.734%	$88.5715	$88.57	$88.55	$88.60
7 purchase totals =	$539.05		$581.4635	$581.47	$581.45	$581.60