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	$82.69	9.222%	$90.3157	$90.32	$90.30	$90.30
Purchase #2	$38.83	13.764%	$44.1746	$44.17	$44.15	$44.20
Purchase #3	$40.70	12.667%	$45.8555	$45.86	$45.85	$45.90
Purchase #4	$91.85	5.434%	$96.8411	$96.84	$96.85	$96.80
Purchase #5	$72.79	11.575%	$81.2154	$81.22	$81.20	$81.20
Purchase #6	$24.25	9.681%	$26.5976	$26.60	$26.60	$26.60
Purchase #7	$79.82	12.291%	$89.6307	$89.63	$89.65	$89.60
7 purchase totals =	$430.93		$474.6306	$474.64	$474.60	$474.60