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	$40.64	12.363%	$45.6643	$45.66	$45.65	$45.70
Purchase #2	$248.87	4.661%	$260.4698	$260.47	$260.45	$260.50
Purchase #3	$141.92	4.846%	$148.7974	$148.80	$148.80	$148.80
Purchase #4	$48.42	9.244%	$52.8959	$52.90	$52.90	$52.90
Purchase #5	$242.73	3.258%	$250.6381	$250.64	$250.65	$250.60
Purchase #6	$78.91	13.486%	$89.5518	$89.55	$89.55	$89.60
Purchase #7	$28.70	13.850%	$32.675	$32.68	$32.70	$32.70
7 purchase totals =	$830.19		$880.6923	$880.70	$880.70	$880.80