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	$86.86	3.672%	$90.0495	$90.05	$90.05	$90.00
Purchase #2	$229.51	11.614%	$256.1653	$256.17	$256.15	$256.20
Purchase #3	$50.93	4.368%	$53.1546	$53.15	$53.15	$53.20
Purchase #4	$27.94	10.616%	$30.9061	$30.91	$30.90	$30.90
Purchase #5	$61.76	7.809%	$66.5828	$66.58	$66.60	$66.60
Purchase #6	$64.86	8.253%	$70.2129	$70.21	$70.20	$70.20
Purchase #7	$106.90	11.706%	$119.4137	$119.41	$119.40	$119.40
7 purchase totals =	$628.76		$686.4849	$686.48	$686.45	$686.50