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	$115.75	9.275%	$126.4858	$126.49	$126.50	$126.50
Purchase #2	$75.27	13.148%	$85.1665	$85.17	$85.15	$85.20
Purchase #3	$13.39	6.850%	$14.3072	$14.31	$14.30	$14.30
Purchase #4	$89.59	11.695%	$100.0676	$100.07	$100.05	$100.10
Purchase #5	$56.35	10.282%	$62.1439	$62.14	$62.15	$62.10
Purchase #6	$169.82	7.623%	$182.7654	$182.77	$182.75	$182.80
Purchase #7	$7.48	4.261%	$7.7987	$7.80	$7.80	$7.80
7 purchase totals =	$527.65		$578.7351	$578.75	$578.70	$578.80