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	$109.38	13.356%	$123.9888	$123.99	$124.00	$124.00
Purchase #2	$85.81	4.383%	$89.5711	$89.57	$89.55	$89.60
Purchase #3	$75.26	10.481%	$83.148	$83.15	$83.15	$83.10
Purchase #4	$126.53	5.648%	$133.6764	$133.68	$133.70	$133.70
Purchase #5	$9.41	7.191%	$10.0867	$10.09	$10.10	$10.10
Purchase #6	$40.61	12.617%	$45.7338	$45.73	$45.75	$45.70
Purchase #7	$66.70	9.794%	$73.2326	$73.23	$73.25	$73.20
7 purchase totals =	$513.70		$559.4374	$559.44	$559.50	$559.40