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	$89.73	11.849%	$100.3621	$100.36	$100.35	$100.40
Purchase #2	$164.82	12.132%	$184.816	$184.82	$184.80	$184.80
Purchase #3	$83.94	9.553%	$91.9588	$91.96	$91.95	$92.00
Purchase #4	$193.68	13.221%	$219.2864	$219.29	$219.30	$219.30
Purchase #5	$231.34	3.426%	$239.2657	$239.27	$239.25	$239.30
Purchase #6	$93.86	5.626%	$99.1406	$99.14	$99.15	$99.10
Purchase #7	$73.92	12.239%	$82.9671	$82.97	$82.95	$83.00
7 purchase totals =	$931.29		$1,017.7967	$1,017.81	$1,017.75	$1,017.90