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	$80.74	11.790%	$90.2592	$90.26	$90.25	$90.30
Purchase #2	$173.54	8.252%	$187.8605	$187.86	$187.85	$187.90
Purchase #3	$12.38	8.653%	$13.4512	$13.45	$13.45	$13.50
Purchase #4	$167.25	9.706%	$183.4833	$183.48	$183.50	$183.50
Purchase #5	$91.96	9.408%	$100.6116	$100.61	$100.60	$100.60
Purchase #6	$67.59	12.781%	$76.2287	$76.23	$76.25	$76.20
Purchase #7	$37.46	11.363%	$41.7166	$41.72	$41.70	$41.70
7 purchase totals =	$630.92		$693.6111	$693.61	$693.60	$693.70