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	$123.36	13.615%	$140.1555	$140.16	$140.15	$140.20
Purchase #2	$193.44	11.605%	$215.8887	$215.89	$215.90	$215.90
Purchase #3	$151.69	10.818%	$168.0998	$168.10	$168.10	$168.10
Purchase #4	$62.80	7.379%	$67.434	$67.43	$67.45	$67.40
Purchase #5	$90.64	6.815%	$96.8171	$96.82	$96.80	$96.80
Purchase #6	$59.80	3.783%	$62.0622	$62.06	$62.05	$62.10
Purchase #7	$139.58	6.305%	$148.3805	$148.38	$148.40	$148.40
7 purchase totals =	$821.31		$898.8378	$898.84	$898.85	$898.90