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	$234.57	6.147%	$248.989	$248.99	$249.00	$249.00
Purchase #2	$78.41	6.164%	$83.2432	$83.24	$83.25	$83.20
Purchase #3	$110.75	11.575%	$123.5693	$123.57	$123.55	$123.60
Purchase #4	$81.49	10.209%	$89.8093	$89.81	$89.80	$89.80
Purchase #5	$215.55	3.344%	$222.758	$222.76	$222.75	$222.80
Purchase #6	$123.57	5.288%	$130.1044	$130.10	$130.10	$130.10
Purchase #7	$131.88	3.189%	$136.0857	$136.09	$136.10	$136.10
7 purchase totals =	$976.22		$1,034.5589	$1,034.56	$1,034.55	$1,034.60