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	$103.67	7.857%	$111.8154	$111.82	$111.80	$111.80
Purchase #2	$225.78	9.146%	$246.4298	$246.43	$246.45	$246.40
Purchase #3	$88.57	11.704%	$98.9362	$98.94	$98.95	$98.90
Purchase #4	$144.85	13.852%	$164.9146	$164.91	$164.90	$164.90
Purchase #5	$67.72	11.390%	$75.4333	$75.43	$75.45	$75.40
Purchase #6	$167.76	6.809%	$179.1828	$179.18	$179.20	$179.20
Purchase #7	$77.55	11.513%	$86.4783	$86.48	$86.50	$86.50
7 purchase totals =	$875.90		$963.1904	$963.19	$963.25	$963.10