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	$234.26	12.610%	$263.8002	$263.80	$263.80	$263.80
Purchase #2	$141.87	10.202%	$156.3436	$156.34	$156.35	$156.30
Purchase #3	$65.44	9.841%	$71.88	$71.88	$71.90	$71.90
Purchase #4	$180.88	7.539%	$194.5165	$194.52	$194.50	$194.50
Purchase #5	$229.88	7.381%	$246.8474	$246.85	$246.85	$246.80
Purchase #6	$103.84	8.768%	$112.9447	$112.94	$112.95	$112.90
Purchase #7	$40.35	5.316%	$42.495	$42.50	$42.50	$42.50
7 purchase totals =	$996.52		$1,088.8274	$1,088.83	$1,088.85	$1,088.70