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	$121.83	12.346%	$136.8711	$136.87	$136.85	$136.90
Purchase #2	$47.36	12.479%	$53.2701	$53.27	$53.25	$53.30
Purchase #3	$9.83	3.706%	$10.1943	$10.19	$10.20	$10.20
Purchase #4	$100.48	10.510%	$111.0404	$111.04	$111.05	$111.00
Purchase #5	$26.76	4.754%	$28.0322	$28.03	$28.05	$28.00
Purchase #6	$79.91	10.614%	$88.3916	$88.39	$88.40	$88.40
Purchase #7	$94.66	13.595%	$107.529	$107.53	$107.55	$107.50
7 purchase totals =	$480.83		$535.3287	$535.32	$535.35	$535.30