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	$88.81	13.152%	$100.4903	$100.49	$100.50	$100.50
Purchase #2	$242.53	3.406%	$250.7906	$250.79	$250.80	$250.80
Purchase #3	$142.54	5.325%	$150.1303	$150.13	$150.15	$150.10
Purchase #4	$126.71	11.379%	$141.1283	$141.13	$141.15	$141.10
Purchase #5	$242.77	8.325%	$262.9806	$262.98	$263.00	$263.00
Purchase #6	$148.70	10.674%	$164.5722	$164.57	$164.55	$164.60
Purchase #7	$8.66	11.261%	$9.6352	$9.64	$9.65	$9.60
7 purchase totals =	$1,000.72		$1,079.7275	$1,079.73	$1,079.80	$1,079.70