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	$172.44	7.462%	$185.3075	$185.31	$185.30	$185.30
Purchase #2	$26.76	6.680%	$28.5476	$28.55	$28.55	$28.50
Purchase #3	$178.33	13.454%	$202.3225	$202.32	$202.30	$202.30
Purchase #4	$113.95	6.593%	$121.4627	$121.46	$121.45	$121.50
Purchase #5	$73.88	13.230%	$83.6543	$83.65	$83.65	$83.70
Purchase #6	$31.28	11.870%	$34.9929	$34.99	$35.00	$35.00
Purchase #7	$10.38	9.242%	$11.3393	$11.34	$11.35	$11.30
7 purchase totals =	$607.02		$667.6268	$667.62	$667.60	$667.60