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	$80.41	10.128%	$88.5539	$88.55	$88.55	$88.60
Purchase #2	$18.64	11.626%	$20.8071	$20.81	$20.80	$20.80
Purchase #3	$167.89	10.763%	$185.96	$185.96	$185.95	$186.00
Purchase #4	$107.44	3.116%	$110.7878	$110.79	$110.80	$110.80
Purchase #5	$200.86	12.430%	$225.8269	$225.83	$225.85	$225.80
Purchase #6	$29.36	11.783%	$32.8195	$32.82	$32.80	$32.80
Purchase #7	$123.72	6.538%	$131.8088	$131.81	$131.80	$131.80
7 purchase totals =	$728.32		$796.5640	$796.57	$796.55	$796.60