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	$196.96	3.774%	$204.3933	$204.39	$204.40	$204.40
Purchase #2	$37.26	5.284%	$39.2288	$39.23	$39.25	$39.20
Purchase #3	$101.90	9.825%	$111.9117	$111.91	$111.90	$111.90
Purchase #4	$139.34	12.195%	$156.3325	$156.33	$156.35	$156.30
Purchase #5	$208.42	9.848%	$228.9452	$228.95	$228.95	$228.90
Purchase #6	$46.28	13.856%	$52.6926	$52.69	$52.70	$52.70
Purchase #7	$182.80	7.416%	$196.3564	$196.36	$196.35	$196.40
7 purchase totals =	$912.96		$989.8605	$989.86	$989.90	$989.80