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	$173.68	3.722%	$180.1444	$180.14	$180.15	$180.10
Purchase #2	$124.93	3.784%	$129.6574	$129.66	$129.65	$129.70
Purchase #3	$86.44	13.725%	$98.3039	$98.30	$98.30	$98.30
Purchase #4	$68.59	3.314%	$70.8631	$70.86	$70.85	$70.90
Purchase #5	$196.66	4.295%	$205.1065	$205.11	$205.10	$205.10
Purchase #6	$104.35	6.708%	$111.3498	$111.35	$111.35	$111.30
Purchase #7	$37.84	13.163%	$42.8209	$42.82	$42.80	$42.80
7 purchase totals =	$792.49		$838.2460	$838.24	$838.20	$838.20