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	$6.96	11.379%	$7.752	$7.75	$7.75	$7.80
Purchase #2	$219.87	10.334%	$242.5914	$242.59	$242.60	$242.60
Purchase #3	$50.77	13.674%	$57.7123	$57.71	$57.70	$57.70
Purchase #4	$104.35	7.802%	$112.4914	$112.49	$112.50	$112.50
Purchase #5	$97.92	10.131%	$107.8403	$107.84	$107.85	$107.80
Purchase #6	$99.75	5.365%	$105.1016	$105.10	$105.10	$105.10
Purchase #7	$180.44	6.127%	$191.4956	$191.50	$191.50	$191.50
7 purchase totals =	$760.06		$824.9846	$824.98	$825.00	$825.00