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	$64.37	5.463%	$67.8865	$67.89	$67.90	$67.90
Purchase #2	$66.53	10.371%	$73.4298	$73.43	$73.45	$73.40
Purchase #3	$166.55	9.829%	$182.9202	$182.92	$182.90	$182.90
Purchase #4	$94.76	8.269%	$102.5957	$102.60	$102.60	$102.60
Purchase #5	$36.74	7.442%	$39.4742	$39.47	$39.45	$39.50
Purchase #6	$111.42	6.709%	$118.8952	$118.90	$118.90	$118.90
Purchase #7	$19.75	13.815%	$22.4785	$22.48	$22.50	$22.50
7 purchase totals =	$560.12		$607.6801	$607.69	$607.70	$607.70