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	$136.88	12.727%	$154.3007	$154.30	$154.30	$154.30
Purchase #2	$73.81	6.520%	$78.6224	$78.62	$78.60	$78.60
Purchase #3	$177.52	12.783%	$200.2124	$200.21	$200.20	$200.20
Purchase #4	$106.64	5.347%	$112.342	$112.34	$112.35	$112.30
Purchase #5	$150.36	3.346%	$155.391	$155.39	$155.40	$155.40
Purchase #6	$150.26	13.215%	$170.1169	$170.12	$170.10	$170.10
Purchase #7	$129.34	10.507%	$142.9298	$142.93	$142.95	$142.90
7 purchase totals =	$924.81		$1,013.9152	$1,013.91	$1,013.90	$1,013.80