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	$5.99	4.383%	$6.2525	$6.25	$6.25	$6.30
Purchase #2	$83.55	7.630%	$89.9249	$89.92	$89.90	$89.90
Purchase #3	$43.86	3.281%	$45.299	$45.30	$45.30	$45.30
Purchase #4	$180.31	5.567%	$190.3479	$190.35	$190.35	$190.30
Purchase #5	$22.71	8.811%	$24.711	$24.71	$24.70	$24.70
Purchase #6	$67.68	5.603%	$71.4721	$71.47	$71.45	$71.50
Purchase #7	$123.51	6.703%	$131.7889	$131.79	$131.80	$131.80
7 purchase totals =	$527.61		$559.7963	$559.79	$559.75	$559.80