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	$46.28	12.708%	$52.1613	$52.16	$52.15	$52.20
Purchase #2	$246.66	12.430%	$277.3198	$277.32	$277.30	$277.30
Purchase #3	$114.50	4.694%	$119.8746	$119.87	$119.85	$119.90
Purchase #4	$67.36	5.496%	$71.0621	$71.06	$71.05	$71.10
Purchase #5	$207.49	7.102%	$222.2259	$222.23	$222.25	$222.20
Purchase #6	$65.66	9.785%	$72.0848	$72.08	$72.10	$72.10
Purchase #7	$74.81	5.448%	$78.8856	$78.89	$78.90	$78.90
7 purchase totals =	$822.76		$893.6141	$893.61	$893.60	$893.70