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	$103.65	13.162%	$117.2924	$117.29	$117.30	$117.30
Purchase #2	$51.33	12.754%	$57.8766	$57.88	$57.90	$57.90
Purchase #3	$41.89	7.558%	$45.056	$45.06	$45.05	$45.10
Purchase #4	$225.78	3.773%	$234.2987	$234.30	$234.30	$234.30
Purchase #5	$168.53	13.657%	$191.5461	$191.55	$191.55	$191.50
Purchase #6	$52.98	3.164%	$54.6563	$54.66	$54.65	$54.70
Purchase #7	$16.50	4.356%	$17.2187	$17.22	$17.20	$17.20
7 purchase totals =	$660.66		$717.9448	$717.96	$717.95	$718.00