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	$123.59	11.388%	$137.6644	$137.66	$137.65	$137.70
Purchase #2	$218.63	11.688%	$244.1835	$244.18	$244.20	$244.20
Purchase #3	$98.29	11.376%	$109.4715	$109.47	$109.45	$109.50
Purchase #4	$106.65	6.834%	$113.9385	$113.94	$113.95	$113.90
Purchase #5	$114.64	3.601%	$118.7682	$118.77	$118.75	$118.80
Purchase #6	$242.75	6.847%	$259.3711	$259.37	$259.35	$259.40
Purchase #7	$42.47	10.520%	$46.9378	$46.94	$46.95	$46.90
7 purchase totals =	$947.02		$1,030.3350	$1,030.33	$1,030.30	$1,030.40