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	$38.47	9.190%	$42.0054	$42.01	$42.00	$42.00
Purchase #2	$94.30	13.774%	$107.2889	$107.29	$107.30	$107.30
Purchase #3	$212.48	7.413%	$228.2311	$228.23	$228.25	$228.20
Purchase #4	$188.86	3.835%	$196.1028	$196.10	$196.10	$196.10
Purchase #5	$17.87	9.824%	$19.6255	$19.63	$19.65	$19.60
Purchase #6	$31.43	13.210%	$35.5819	$35.58	$35.60	$35.60
Purchase #7	$67.29	7.108%	$72.073	$72.07	$72.05	$72.10
7 purchase totals =	$650.70		$700.9086	$700.91	$700.95	$700.90