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	$75.94	9.309%	$83.0093	$83.01	$83.00	$83.00
Purchase #2	$9.84	4.813%	$10.3136	$10.31	$10.30	$10.30
Purchase #3	$91.60	10.162%	$100.9084	$100.91	$100.90	$100.90
Purchase #4	$33.37	8.670%	$36.2632	$36.26	$36.25	$36.30
Purchase #5	$97.51	5.305%	$102.6829	$102.68	$102.70	$102.70
Purchase #6	$57.31	3.812%	$59.4947	$59.49	$59.50	$59.50
Purchase #7	$52.98	8.256%	$57.354	$57.35	$57.35	$57.40
7 purchase totals =	$418.55		$450.0261	$450.01	$450.00	$450.10