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	$33.59	12.720%	$37.8626	$37.86	$37.85	$37.90
Purchase #2	$61.72	13.471%	$70.0343	$70.03	$70.05	$70.00
Purchase #3	$6.75	9.669%	$7.4027	$7.40	$7.40	$7.40
Purchase #4	$62.66	4.783%	$65.657	$65.66	$65.65	$65.70
Purchase #5	$85.69	10.177%	$94.4107	$94.41	$94.40	$94.40
Purchase #6	$35.51	10.667%	$39.2979	$39.30	$39.30	$39.30
Purchase #7	$194.48	10.714%	$215.3166	$215.32	$215.30	$215.30
7 purchase totals =	$480.40		$529.9818	$529.98	$529.95	$530.00