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	$64.53	10.460%	$71.2798	$71.28	$71.30	$71.30
Purchase #2	$240.55	6.474%	$256.1232	$256.12	$256.10	$256.10
Purchase #3	$50.68	12.221%	$56.8736	$56.87	$56.85	$56.90
Purchase #4	$129.52	6.294%	$137.672	$137.67	$137.65	$137.70
Purchase #5	$90.62	9.794%	$99.4953	$99.50	$99.50	$99.50
Purchase #6	$96.76	8.526%	$105.0098	$105.01	$105.00	$105.00
Purchase #7	$152.51	6.462%	$162.3652	$162.37	$162.35	$162.40
7 purchase totals =	$825.17		$888.8189	$888.82	$888.75	$888.90