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	$237.64	12.847%	$268.1696	$268.17	$268.15	$268.20
Purchase #2	$88.89	8.335%	$96.299	$96.30	$96.30	$96.30
Purchase #3	$239.58	12.258%	$268.9477	$268.95	$268.95	$268.90
Purchase #4	$237.72	10.748%	$263.2701	$263.27	$263.25	$263.30
Purchase #5	$119.79	9.838%	$131.5749	$131.57	$131.55	$131.60
Purchase #6	$75.50	4.441%	$78.853	$78.85	$78.85	$78.90
Purchase #7	$160.40	7.270%	$172.0611	$172.06	$172.05	$172.10
7 purchase totals =	$1,159.52		$1,279.1754	$1,279.17	$1,279.10	$1,279.30