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	$178.83	4.661%	$187.1653	$187.17	$187.15	$187.20
Purchase #2	$206.38	10.795%	$228.6587	$228.66	$228.65	$228.70
Purchase #3	$132.89	11.760%	$148.5179	$148.52	$148.50	$148.50
Purchase #4	$23.44	12.598%	$26.393	$26.39	$26.40	$26.40
Purchase #5	$166.27	3.393%	$171.9115	$171.91	$171.90	$171.90
Purchase #6	$63.98	4.508%	$66.8642	$66.86	$66.85	$66.90
Purchase #7	$88.67	13.707%	$100.824	$100.82	$100.80	$100.80
7 purchase totals =	$860.46		$930.3346	$930.33	$930.25	$930.40