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	$86.32	9.385%	$94.4211	$94.42	$94.40	$94.40
Purchase #2	$32.72	12.215%	$36.7167	$36.72	$36.70	$36.70
Purchase #3	$82.89	8.579%	$90.0011	$90.00	$90.00	$90.00
Purchase #4	$88.75	6.232%	$94.2809	$94.28	$94.30	$94.30
Purchase #5	$203.37	9.575%	$222.8427	$222.84	$222.85	$222.80
Purchase #6	$244.42	10.644%	$270.4361	$270.44	$270.45	$270.40
Purchase #7	$10.42	9.567%	$11.4169	$11.42	$11.40	$11.40
7 purchase totals =	$748.89		$820.1155	$820.12	$820.10	$820.00