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	$150.50	3.293%	$155.456	$155.46	$155.45	$155.50
Purchase #2	$213.31	3.560%	$220.9038	$220.90	$220.90	$220.90
Purchase #3	$24.41	13.710%	$27.7566	$27.76	$27.75	$27.80
Purchase #4	$199.78	8.819%	$217.3986	$217.40	$217.40	$217.40
Purchase #5	$36.71	8.488%	$39.8259	$39.83	$39.85	$39.80
Purchase #6	$79.44	13.486%	$90.1533	$90.15	$90.15	$90.20
Purchase #7	$55.48	4.264%	$57.8457	$57.85	$57.85	$57.80
7 purchase totals =	$759.63		$809.3399	$809.35	$809.35	$809.40