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	$48.76	11.584%	$54.4084	$54.41	$54.40	$54.40
Purchase #2	$150.62	6.186%	$159.9374	$159.94	$159.95	$159.90
Purchase #3	$118.37	5.206%	$124.5323	$124.53	$124.55	$124.50
Purchase #4	$50.50	7.609%	$54.3425	$54.34	$54.35	$54.30
Purchase #5	$241.58	13.229%	$273.5386	$273.54	$273.55	$273.50
Purchase #6	$33.45	7.304%	$35.8932	$35.89	$35.90	$35.90
Purchase #7	$53.25	7.636%	$57.3162	$57.32	$57.30	$57.30
7 purchase totals =	$696.53		$759.9686	$759.97	$760.00	$759.80