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	$142.95	8.760%	$155.4724	$155.47	$155.45	$155.50
Purchase #2	$46.81	13.372%	$53.0694	$53.07	$53.05	$53.10
Purchase #3	$172.83	7.111%	$185.1199	$185.12	$185.10	$185.10
Purchase #4	$121.46	10.804%	$134.5825	$134.58	$134.60	$134.60
Purchase #5	$28.77	8.444%	$31.1993	$31.20	$31.20	$31.20
Purchase #6	$78.32	12.508%	$88.1163	$88.12	$88.10	$88.10
Purchase #7	$47.44	12.300%	$53.2751	$53.28	$53.30	$53.30
7 purchase totals =	$638.58		$700.8349	$700.84	$700.80	$700.90