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	$250.70	6.131%	$266.0704	$266.07	$266.05	$266.10
Purchase #2	$49.89	4.619%	$52.1944	$52.19	$52.20	$52.20
Purchase #3	$178.75	13.849%	$203.5051	$203.51	$203.50	$203.50
Purchase #4	$38.78	9.699%	$42.5413	$42.54	$42.55	$42.50
Purchase #5	$82.28	9.872%	$90.4027	$90.40	$90.40	$90.40
Purchase #6	$78.76	6.613%	$83.9684	$83.97	$83.95	$84.00
Purchase #7	$18.91	4.369%	$19.7362	$19.74	$19.75	$19.70
7 purchase totals =	$698.07		$758.4185	$758.42	$758.40	$758.40