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	$96.94	7.834%	$104.5343	$104.53	$104.55	$104.50
Purchase #2	$203.71	12.562%	$229.3001	$229.30	$229.30	$229.30
Purchase #3	$170.93	8.164%	$184.8847	$184.88	$184.90	$184.90
Purchase #4	$121.25	4.855%	$127.1367	$127.14	$127.15	$127.10
Purchase #5	$78.91	5.568%	$83.3037	$83.30	$83.30	$83.30
Purchase #6	$128.77	8.692%	$139.9627	$139.96	$139.95	$140.00
Purchase #7	$46.36	9.757%	$50.8833	$50.88	$50.90	$50.90
7 purchase totals =	$846.87		$920.0055	$919.99	$920.05	$920.00