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	$99.41	12.448%	$111.7846	$111.78	$111.80	$111.80
Purchase #2	$122.82	13.167%	$138.9917	$138.99	$139.00	$139.00
Purchase #3	$205.99	3.662%	$213.5334	$213.53	$213.55	$213.50
Purchase #4	$150.55	6.375%	$160.1476	$160.15	$160.15	$160.10
Purchase #5	$47.31	12.406%	$53.1793	$53.18	$53.20	$53.20
Purchase #6	$135.48	12.217%	$152.0316	$152.03	$152.05	$152.00
Purchase #7	$81.54	11.280%	$90.7377	$90.74	$90.75	$90.70
7 purchase totals =	$843.10		$920.4059	$920.40	$920.50	$920.30