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	$148.51	6.650%	$158.3859	$158.39	$158.40	$158.40
Purchase #2	$167.73	10.873%	$185.9673	$185.97	$185.95	$186.00
Purchase #3	$249.78	13.671%	$283.9274	$283.93	$283.95	$283.90
Purchase #4	$80.31	11.451%	$89.5063	$89.51	$89.50	$89.50
Purchase #5	$247.72	9.160%	$270.4112	$270.41	$270.40	$270.40
Purchase #6	$31.36	11.118%	$34.8466	$34.85	$34.85	$34.80
Purchase #7	$215.37	6.555%	$229.4875	$229.49	$229.50	$229.50
7 purchase totals =	$1,140.78		$1,252.5322	$1,252.55	$1,252.55	$1,252.50