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	$72.66	7.764%	$78.3013	$78.30	$78.30	$78.30
Purchase #2	$190.43	4.384%	$198.7785	$198.78	$198.80	$198.80
Purchase #3	$11.64	3.507%	$12.0482	$12.05	$12.05	$12.00
Purchase #4	$19.52	10.190%	$21.5091	$21.51	$21.50	$21.50
Purchase #5	$200.36	10.549%	$221.496	$221.50	$221.50	$221.50
Purchase #6	$55.98	4.150%	$58.3032	$58.30	$58.30	$58.30
Purchase #7	$224.55	10.593%	$248.3366	$248.34	$248.35	$248.30
7 purchase totals =	$775.14		$838.7729	$838.78	$838.80	$838.70