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	$138.81	12.642%	$156.3584	$156.36	$156.35	$156.40
Purchase #2	$34.80	6.603%	$37.0978	$37.10	$37.10	$37.10
Purchase #3	$26.26	12.770%	$29.6134	$29.61	$29.60	$29.60
Purchase #4	$5.78	6.642%	$6.1639	$6.16	$6.15	$6.20
Purchase #5	$53.56	5.637%	$56.5792	$56.58	$56.60	$56.60
Purchase #6	$28.68	12.657%	$32.31	$32.31	$32.30	$32.30
Purchase #7	$110.51	13.549%	$125.483	$125.48	$125.50	$125.50
7 purchase totals =	$398.40		$443.6057	$443.60	$443.60	$443.70