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	$5.32	7.570%	$5.7227	$5.72	$5.70	$5.70
Purchase #2	$73.46	6.462%	$78.207	$78.21	$78.20	$78.20
Purchase #3	$159.85	5.266%	$168.2677	$168.27	$168.25	$168.30
Purchase #4	$49.91	9.325%	$54.5641	$54.56	$54.55	$54.60
Purchase #5	$222.75	10.700%	$246.5843	$246.58	$246.60	$246.60
Purchase #6	$58.32	8.688%	$63.3868	$63.39	$63.40	$63.40
Purchase #7	$149.57	10.614%	$165.4454	$165.45	$165.45	$165.40
7 purchase totals =	$719.18		$782.1780	$782.18	$782.15	$782.20