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	$44.46	13.219%	$50.3372	$50.34	$50.35	$50.30
Purchase #2	$122.75	9.559%	$134.4837	$134.48	$134.50	$134.50
Purchase #3	$76.90	12.798%	$86.7417	$86.74	$86.75	$86.70
Purchase #4	$38.89	11.346%	$43.3025	$43.30	$43.30	$43.30
Purchase #5	$50.83	8.828%	$55.3173	$55.32	$55.30	$55.30
Purchase #6	$153.84	4.203%	$160.3059	$160.31	$160.30	$160.30
Purchase #7	$124.92	5.424%	$131.6957	$131.70	$131.70	$131.70
7 purchase totals =	$612.59		$662.1840	$662.19	$662.20	$662.10