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	$30.45	11.673%	$34.0044	$34.00	$34.00	$34.00
Purchase #2	$77.44	10.248%	$85.3761	$85.38	$85.40	$85.40
Purchase #3	$99.52	4.180%	$103.6799	$103.68	$103.70	$103.70
Purchase #4	$71.59	13.252%	$81.0771	$81.08	$81.10	$81.10
Purchase #5	$148.46	7.410%	$159.4609	$159.46	$159.45	$159.50
Purchase #6	$86.36	3.479%	$89.3645	$89.36	$89.35	$89.40
Purchase #7	$9.53	9.614%	$10.4462	$10.45	$10.45	$10.40
7 purchase totals =	$523.35		$563.4091	$563.41	$563.45	$563.50