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	$58.83	12.453%	$66.1561	$66.16	$66.15	$66.20
Purchase #2	$188.32	8.566%	$204.4515	$204.45	$204.45	$204.50
Purchase #3	$74.56	10.726%	$82.5573	$82.56	$82.55	$82.60
Purchase #4	$105.45	12.194%	$118.3086	$118.31	$118.30	$118.30
Purchase #5	$114.98	11.349%	$128.0291	$128.03	$128.05	$128.00
Purchase #6	$137.88	3.275%	$142.3956	$142.40	$142.40	$142.40
Purchase #7	$159.46	9.450%	$174.529	$174.53	$174.55	$174.50
7 purchase totals =	$839.48		$916.4272	$916.44	$916.45	$916.50