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	$246.83	4.516%	$257.9768	$257.98	$258.00	$258.00
Purchase #2	$55.25	10.201%	$60.8861	$60.89	$60.90	$60.90
Purchase #3	$99.39	12.376%	$111.6905	$111.69	$111.70	$111.70
Purchase #4	$199.34	10.632%	$220.5338	$220.53	$220.55	$220.50
Purchase #5	$91.92	7.606%	$98.9114	$98.91	$98.90	$98.90
Purchase #6	$107.54	7.316%	$115.4076	$115.41	$115.40	$115.40
Purchase #7	$113.26	12.686%	$127.6282	$127.63	$127.65	$127.60
7 purchase totals =	$913.53		$993.0344	$993.04	$993.10	$993.00