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	$121.88	5.680%	$128.8028	$128.80	$128.80	$128.80
Purchase #2	$58.91	12.793%	$66.4464	$66.45	$66.45	$66.40
Purchase #3	$33.56	4.731%	$35.1477	$35.15	$35.15	$35.10
Purchase #4	$142.65	3.628%	$147.8253	$147.83	$147.85	$147.80
Purchase #5	$31.75	3.293%	$32.7955	$32.80	$32.80	$32.80
Purchase #6	$37.55	9.534%	$41.13	$41.13	$41.15	$41.10
Purchase #7	$65.55	9.240%	$71.6068	$71.61	$71.60	$71.60
7 purchase totals =	$491.85		$523.7545	$523.77	$523.80	$523.60