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	$144.86	10.322%	$159.8124	$159.81	$159.80	$159.80
Purchase #2	$223.92	6.240%	$237.8926	$237.89	$237.90	$237.90
Purchase #3	$181.59	5.198%	$191.029	$191.03	$191.05	$191.00
Purchase #4	$80.34	12.576%	$90.4436	$90.44	$90.45	$90.40
Purchase #5	$240.53	10.820%	$266.5553	$266.56	$266.55	$266.60
Purchase #6	$50.35	13.633%	$57.2142	$57.21	$57.20	$57.20
Purchase #7	$12.97	11.160%	$14.4175	$14.42	$14.40	$14.40
7 purchase totals =	$934.56		$1,017.3646	$1,017.36	$1,017.35	$1,017.30