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	$133.29	8.617%	$144.7756	$144.78	$144.80	$144.80
Purchase #2	$21.41	12.142%	$24.0096	$24.01	$24.00	$24.00
Purchase #3	$6.70	8.185%	$7.2484	$7.25	$7.25	$7.20
Purchase #4	$247.80	6.710%	$264.4274	$264.43	$264.45	$264.40
Purchase #5	$212.57	8.450%	$230.5322	$230.53	$230.55	$230.50
Purchase #6	$159.59	5.857%	$168.9372	$168.94	$168.95	$168.90
Purchase #7	$245.35	10.627%	$271.4233	$271.42	$271.40	$271.40
7 purchase totals =	$1,026.71		$1,111.3537	$1,111.36	$1,111.40	$1,111.20