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	$222.36	7.858%	$239.833	$239.83	$239.85	$239.80
Purchase #2	$79.84	4.510%	$83.4408	$83.44	$83.45	$83.40
Purchase #3	$155.46	4.147%	$161.9069	$161.91	$161.90	$161.90
Purchase #4	$75.96	8.355%	$82.3065	$82.31	$82.30	$82.30
Purchase #5	$172.89	6.726%	$184.5186	$184.52	$184.50	$184.50
Purchase #6	$151.29	8.480%	$164.1194	$164.12	$164.10	$164.10
Purchase #7	$82.50	9.346%	$90.2105	$90.21	$90.20	$90.20
7 purchase totals =	$940.30		$1,006.3357	$1,006.34	$1,006.30	$1,006.20