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	$35.66	8.152%	$38.567	$38.57	$38.55	$38.60
Purchase #2	$223.96	8.699%	$243.4423	$243.44	$243.45	$243.40
Purchase #3	$35.69	5.144%	$37.5259	$37.53	$37.55	$37.50
Purchase #4	$86.89	3.492%	$89.9242	$89.92	$89.90	$89.90
Purchase #5	$105.88	11.305%	$117.8497	$117.85	$117.85	$117.80
Purchase #6	$37.31	3.677%	$38.6819	$38.68	$38.70	$38.70
Purchase #7	$55.64	12.602%	$62.6518	$62.65	$62.65	$62.70
7 purchase totals =	$581.03		$628.6428	$628.64	$628.65	$628.60