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	$89.93	10.409%	$99.2908	$99.29	$99.30	$99.30
Purchase #2	$86.44	3.336%	$89.3236	$89.32	$89.30	$89.30
Purchase #3	$72.61	10.404%	$80.1643	$80.16	$80.15	$80.20
Purchase #4	$114.49	12.144%	$128.3937	$128.39	$128.40	$128.40
Purchase #5	$139.46	10.815%	$154.5426	$154.54	$154.55	$154.50
Purchase #6	$15.55	5.773%	$16.4477	$16.45	$16.45	$16.40
Purchase #7	$156.54	11.258%	$174.1633	$174.16	$174.15	$174.20
7 purchase totals =	$675.02		$742.3260	$742.31	$742.30	$742.30