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	$17.72	13.307%	$20.078	$20.08	$20.10	$20.10
Purchase #2	$209.75	8.363%	$227.2914	$227.29	$227.30	$227.30
Purchase #3	$195.76	13.496%	$222.1798	$222.18	$222.20	$222.20
Purchase #4	$50.39	6.179%	$53.5036	$53.50	$53.50	$53.50
Purchase #5	$218.65	13.318%	$247.7698	$247.77	$247.75	$247.80
Purchase #6	$65.40	3.734%	$67.842	$67.84	$67.85	$67.80
Purchase #7	$89.37	10.244%	$98.5251	$98.53	$98.55	$98.50
7 purchase totals =	$847.04		$937.1897	$937.19	$937.25	$937.20