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	$190.71	5.133%	$200.4991	$200.50	$200.50	$200.50
Purchase #2	$69.61	4.198%	$72.5322	$72.53	$72.55	$72.50
Purchase #3	$205.94	9.415%	$225.3293	$225.33	$225.35	$225.30
Purchase #4	$92.75	11.551%	$103.4636	$103.46	$103.45	$103.50
Purchase #5	$185.51	12.797%	$209.2497	$209.25	$209.25	$209.20
Purchase #6	$30.59	4.794%	$32.0565	$32.06	$32.05	$32.10
Purchase #7	$122.82	9.753%	$134.7986	$134.80	$134.80	$134.80
7 purchase totals =	$897.93		$977.9290	$977.93	$977.95	$977.90