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	$115.25	4.245%	$120.1424	$120.14	$120.15	$120.10
Purchase #2	$198.52	12.151%	$222.6422	$222.64	$222.65	$222.60
Purchase #3	$86.84	11.873%	$97.1505	$97.15	$97.15	$97.20
Purchase #4	$35.59	13.595%	$40.4285	$40.43	$40.45	$40.40
Purchase #5	$201.45	9.102%	$219.786	$219.79	$219.80	$219.80
Purchase #6	$238.56	12.298%	$267.8981	$267.90	$267.90	$267.90
Purchase #7	$184.94	8.318%	$200.3233	$200.32	$200.30	$200.30
7 purchase totals =	$1,061.15		$1,168.3710	$1,168.37	$1,168.40	$1,168.30