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	$29.43	13.308%	$33.3465	$33.35	$33.35	$33.30
Purchase #2	$67.59	13.654%	$76.8187	$76.82	$76.80	$76.80
Purchase #3	$33.91	11.221%	$37.715	$37.72	$37.70	$37.70
Purchase #4	$12.40	6.310%	$13.1824	$13.18	$13.20	$13.20
Purchase #5	$189.82	13.756%	$215.9316	$215.93	$215.95	$215.90
Purchase #6	$191.28	8.750%	$208.017	$208.02	$208.00	$208.00
Purchase #7	$207.88	8.452%	$225.45	$225.45	$225.45	$225.50
7 purchase totals =	$732.31		$810.4612	$810.47	$810.45	$810.40