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	$64.28	12.246%	$72.1517	$72.15	$72.15	$72.20
Purchase #2	$40.66	12.212%	$45.6254	$45.63	$45.65	$45.60
Purchase #3	$217.41	3.471%	$224.9563	$224.96	$224.95	$225.00
Purchase #4	$22.84	9.699%	$25.0553	$25.06	$25.05	$25.10
Purchase #5	$166.40	12.550%	$187.2832	$187.28	$187.30	$187.30
Purchase #6	$42.36	7.365%	$45.4798	$45.48	$45.50	$45.50
Purchase #7	$158.57	13.500%	$179.977	$179.98	$180.00	$180.00
7 purchase totals =	$712.52		$780.5287	$780.54	$780.60	$780.70