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	$27.60	3.396%	$28.5373	$28.54	$28.55	$28.50
Purchase #2	$135.29	11.327%	$150.6143	$150.61	$150.60	$150.60
Purchase #3	$35.28	10.328%	$38.9237	$38.92	$38.90	$38.90
Purchase #4	$214.35	9.704%	$235.1505	$235.15	$235.15	$235.20
Purchase #5	$175.35	9.234%	$191.5418	$191.54	$191.55	$191.50
Purchase #6	$220.58	10.569%	$243.8931	$243.89	$243.90	$243.90
Purchase #7	$67.83	13.275%	$76.8344	$76.83	$76.85	$76.80
7 purchase totals =	$876.28		$965.4951	$965.48	$965.50	$965.40