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	$25.85	11.823%	$28.9062	$28.91	$28.90	$28.90
Purchase #2	$234.73	3.123%	$242.0606	$242.06	$242.05	$242.10
Purchase #3	$166.59	3.574%	$172.5439	$172.54	$172.55	$172.50
Purchase #4	$159.56	13.562%	$181.1995	$181.20	$181.20	$181.20
Purchase #5	$130.65	8.435%	$141.6703	$141.67	$141.65	$141.70
Purchase #6	$85.72	5.438%	$90.3815	$90.38	$90.40	$90.40
Purchase #7	$144.82	7.818%	$156.142	$156.14	$156.15	$156.10
7 purchase totals =	$947.92		$1,012.9040	$1,012.90	$1,012.90	$1,012.90