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	$18.59	10.285%	$20.502	$20.50	$20.50	$20.50
Purchase #2	$155.76	12.598%	$175.3826	$175.38	$175.40	$175.40
Purchase #3	$25.46	8.639%	$27.6595	$27.66	$27.65	$27.70
Purchase #4	$105.44	10.659%	$116.6788	$116.68	$116.70	$116.70
Purchase #5	$56.69	10.446%	$62.6118	$62.61	$62.60	$62.60
Purchase #6	$94.66	13.197%	$107.1523	$107.15	$107.15	$107.20
Purchase #7	$170.67	8.650%	$185.433	$185.43	$185.45	$185.40
7 purchase totals =	$627.27		$695.4200	$695.41	$695.45	$695.50