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	$30.33	5.836%	$32.1001	$32.10	$32.10	$32.10
Purchase #2	$145.76	3.559%	$150.9476	$150.95	$150.95	$150.90
Purchase #3	$183.35	7.319%	$196.7694	$196.77	$196.75	$196.80
Purchase #4	$56.39	10.444%	$62.2794	$62.28	$62.30	$62.30
Purchase #5	$147.51	4.154%	$153.6376	$153.64	$153.65	$153.60
Purchase #6	$85.62	6.761%	$91.4088	$91.41	$91.40	$91.40
Purchase #7	$74.92	8.417%	$81.226	$81.23	$81.25	$81.20
7 purchase totals =	$723.88		$768.3689	$768.38	$768.40	$768.30