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	$74.99	11.496%	$83.6109	$83.61	$83.60	$83.60
Purchase #2	$247.50	3.132%	$255.2517	$255.25	$255.25	$255.30
Purchase #3	$47.33	4.619%	$49.5162	$49.52	$49.50	$49.50
Purchase #4	$221.90	12.809%	$250.3232	$250.32	$250.30	$250.30
Purchase #5	$172.68	4.719%	$180.8288	$180.83	$180.85	$180.80
Purchase #6	$183.96	6.302%	$195.5532	$195.55	$195.55	$195.60
Purchase #7	$234.94	12.321%	$263.887	$263.89	$263.90	$263.90
7 purchase totals =	$1,183.30		$1,278.9710	$1,278.97	$1,278.95	$1,279.00