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	$169.82	8.823%	$184.8032	$184.80	$184.80	$184.80
Purchase #2	$71.40	3.237%	$73.7112	$73.71	$73.70	$73.70
Purchase #3	$191.30	7.349%	$205.3586	$205.36	$205.35	$205.40
Purchase #4	$142.60	4.305%	$148.7389	$148.74	$148.75	$148.70
Purchase #5	$220.33	13.704%	$250.524	$250.52	$250.50	$250.50
Purchase #6	$71.38	10.525%	$78.8927	$78.89	$78.90	$78.90
Purchase #7	$46.49	10.276%	$51.2673	$51.27	$51.25	$51.30
7 purchase totals =	$913.32		$993.2959	$993.29	$993.25	$993.30