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	$224.37	11.732%	$250.6931	$250.69	$250.70	$250.70
Purchase #2	$171.49	3.501%	$177.4939	$177.49	$177.50	$177.50
Purchase #3	$38.85	9.275%	$42.4533	$42.45	$42.45	$42.50
Purchase #4	$82.58	4.510%	$86.3044	$86.30	$86.30	$86.30
Purchase #5	$34.33	13.290%	$38.8925	$38.89	$38.90	$38.90
Purchase #6	$166.85	11.570%	$186.1545	$186.15	$186.15	$186.20
Purchase #7	$12.65	9.290%	$13.8252	$13.83	$13.85	$13.80
7 purchase totals =	$731.12		$795.8169	$795.80	$795.85	$795.90