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	$51.48	3.460%	$53.2612	$53.26	$53.25	$53.30
Purchase #2	$183.99	5.223%	$193.5998	$193.60	$193.60	$193.60
Purchase #3	$185.69	13.407%	$210.5855	$210.59	$210.60	$210.60
Purchase #4	$167.47	5.152%	$176.0981	$176.10	$176.10	$176.10
Purchase #5	$78.57	13.482%	$89.1628	$89.16	$89.15	$89.20
Purchase #6	$108.59	10.391%	$119.8736	$119.87	$119.85	$119.90
Purchase #7	$231.51	11.115%	$257.2423	$257.24	$257.25	$257.20
7 purchase totals =	$1,007.30		$1,099.8233	$1,099.82	$1,099.80	$1,099.90