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	$67.72	10.401%	$74.7636	$74.76	$74.75	$74.80
Purchase #2	$99.66	12.858%	$112.4743	$112.47	$112.45	$112.50
Purchase #3	$90.70	8.469%	$98.3814	$98.38	$98.40	$98.40
Purchase #4	$5.69	3.830%	$5.9079	$5.91	$5.90	$5.90
Purchase #5	$233.43	13.268%	$264.4015	$264.40	$264.40	$264.40
Purchase #6	$103.49	5.321%	$108.9967	$109.00	$109.00	$109.00
Purchase #7	$54.92	9.107%	$59.9216	$59.92	$59.90	$59.90
7 purchase totals =	$655.61		$724.8470	$724.84	$724.80	$724.90