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	$75.55	11.550%	$84.276	$84.28	$84.30	$84.30
Purchase #2	$132.54	11.509%	$147.794	$147.79	$147.80	$147.80
Purchase #3	$141.33	4.843%	$148.1746	$148.17	$148.15	$148.20
Purchase #4	$165.78	13.638%	$188.3891	$188.39	$188.40	$188.40
Purchase #5	$90.94	10.140%	$100.1613	$100.16	$100.15	$100.20
Purchase #6	$61.41	4.503%	$64.1753	$64.18	$64.20	$64.20
Purchase #7	$168.73	4.819%	$176.8611	$176.86	$176.85	$176.90
7 purchase totals =	$836.28		$909.8314	$909.83	$909.85	$910.00