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	$91.70	9.368%	$100.2905	$100.29	$100.30	$100.30
Purchase #2	$75.38	9.312%	$82.3994	$82.40	$82.40	$82.40
Purchase #3	$28.36	10.194%	$31.251	$31.25	$31.25	$31.30
Purchase #4	$173.53	8.675%	$188.5837	$188.58	$188.60	$188.60
Purchase #5	$105.49	8.857%	$114.8332	$114.83	$114.85	$114.80
Purchase #6	$159.78	5.229%	$168.1349	$168.13	$168.15	$168.10
Purchase #7	$195.36	4.501%	$204.1532	$204.15	$204.15	$204.20
7 purchase totals =	$829.60		$889.6459	$889.63	$889.70	$889.70