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	$245.54	10.579%	$271.5157	$271.52	$271.50	$271.50
Purchase #2	$34.38	3.285%	$35.5094	$35.51	$35.50	$35.50
Purchase #3	$187.56	9.625%	$205.6127	$205.61	$205.60	$205.60
Purchase #4	$30.72	10.143%	$33.8359	$33.84	$33.85	$33.80
Purchase #5	$28.79	9.748%	$31.5964	$31.60	$31.60	$31.60
Purchase #6	$162.25	13.154%	$183.5924	$183.59	$183.60	$183.60
Purchase #7	$105.37	3.194%	$108.7355	$108.74	$108.75	$108.70
7 purchase totals =	$794.61		$870.3980	$870.41	$870.40	$870.30