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	$243.63	11.585%	$271.8545	$271.85	$271.85	$271.90
Purchase #2	$54.91	7.758%	$59.1699	$59.17	$59.15	$59.20
Purchase #3	$202.31	12.707%	$228.0175	$228.02	$228.00	$228.00
Purchase #4	$90.85	11.192%	$101.0179	$101.02	$101.00	$101.00
Purchase #5	$88.52	11.388%	$98.6007	$98.60	$98.60	$98.60
Purchase #6	$171.90	6.822%	$183.627	$183.63	$183.65	$183.60
Purchase #7	$220.60	3.723%	$228.8129	$228.81	$228.80	$228.80
7 purchase totals =	$1,072.72		$1,171.1004	$1,171.10	$1,171.05	$1,171.10