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	$131.55	11.360%	$146.4941	$146.49	$146.50	$146.50
Purchase #2	$203.29	8.179%	$219.9171	$219.92	$219.90	$219.90
Purchase #3	$86.40	3.154%	$89.1251	$89.13	$89.15	$89.10
Purchase #4	$86.61	13.453%	$98.2616	$98.26	$98.25	$98.30
Purchase #5	$142.32	6.418%	$151.4541	$151.45	$151.45	$151.50
Purchase #6	$213.42	3.155%	$220.1534	$220.15	$220.15	$220.20
Purchase #7	$149.51	5.413%	$157.603	$157.60	$157.60	$157.60
7 purchase totals =	$1,013.10		$1,083.0084	$1,083.00	$1,083.00	$1,083.10