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	$205.64	8.531%	$223.1831	$223.18	$223.20	$223.20
Purchase #2	$73.25	4.227%	$76.3463	$76.35	$76.35	$76.30
Purchase #3	$76.55	9.136%	$83.5436	$83.54	$83.55	$83.50
Purchase #4	$64.74	12.237%	$72.6622	$72.66	$72.65	$72.70
Purchase #5	$86.54	4.815%	$90.7069	$90.71	$90.70	$90.70
Purchase #6	$82.59	4.714%	$86.4833	$86.48	$86.50	$86.50
Purchase #7	$40.86	11.340%	$45.4935	$45.49	$45.50	$45.50
7 purchase totals =	$630.17		$678.4189	$678.41	$678.45	$678.40