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	$198.62	8.631%	$215.7629	$215.76	$215.75	$215.80
Purchase #2	$141.50	12.241%	$158.821	$158.82	$158.80	$158.80
Purchase #3	$208.59	8.567%	$226.4599	$226.46	$226.45	$226.50
Purchase #4	$173.73	5.677%	$183.5927	$183.59	$183.60	$183.60
Purchase #5	$190.78	3.162%	$196.8125	$196.81	$196.80	$196.80
Purchase #6	$31.53	11.502%	$35.1566	$35.16	$35.15	$35.20
Purchase #7	$60.71	10.539%	$67.1082	$67.11	$67.10	$67.10
7 purchase totals =	$1,005.46		$1,083.7138	$1,083.71	$1,083.65	$1,083.80