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	$248.55	6.635%	$265.0413	$265.04	$265.05	$265.00
Purchase #2	$50.71	7.663%	$54.5959	$54.60	$54.60	$54.60
Purchase #3	$70.42	11.750%	$78.6944	$78.69	$78.70	$78.70
Purchase #4	$28.83	10.807%	$31.9457	$31.95	$31.95	$31.90
Purchase #5	$179.74	7.484%	$193.1917	$193.19	$193.20	$193.20
Purchase #6	$67.91	7.419%	$72.9482	$72.95	$72.95	$72.90
Purchase #7	$75.71	6.205%	$80.4078	$80.41	$80.40	$80.40
7 purchase totals =	$721.87		$776.8250	$776.83	$776.85	$776.70