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	$139.56	9.203%	$152.4037	$152.40	$152.40	$152.40
Purchase #2	$173.51	9.571%	$190.1166	$190.12	$190.10	$190.10
Purchase #3	$102.75	11.843%	$114.9187	$114.92	$114.90	$114.90
Purchase #4	$78.41	5.159%	$82.4552	$82.46	$82.45	$82.50
Purchase #5	$105.77	7.492%	$113.6943	$113.69	$113.70	$113.70
Purchase #6	$6.98	4.839%	$7.3178	$7.32	$7.30	$7.30
Purchase #7	$5.97	13.415%	$6.7709	$6.77	$6.75	$6.80
7 purchase totals =	$612.95		$667.6772	$667.68	$667.60	$667.70