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	$108.69	8.709%	$118.1558	$118.16	$118.15	$118.20
Purchase #2	$228.31	12.103%	$255.9424	$255.94	$255.95	$255.90
Purchase #3	$53.35	11.512%	$59.4917	$59.49	$59.50	$59.50
Purchase #4	$241.35	5.794%	$255.3338	$255.33	$255.35	$255.30
Purchase #5	$164.25	7.767%	$177.0073	$177.01	$177.00	$177.00
Purchase #6	$82.35	8.839%	$89.6289	$89.63	$89.65	$89.60
Purchase #7	$125.29	8.772%	$136.2804	$136.28	$136.30	$136.30
7 purchase totals =	$1,003.59		$1,091.8403	$1,091.84	$1,091.90	$1,091.80