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	$70.33	10.196%	$77.5008	$77.50	$77.50	$77.50
Purchase #2	$14.68	3.295%	$15.1637	$15.16	$15.15	$15.20
Purchase #3	$122.86	11.839%	$137.4054	$137.41	$137.40	$137.40
Purchase #4	$213.67	12.703%	$240.8125	$240.81	$240.80	$240.80
Purchase #5	$182.86	6.767%	$195.2341	$195.23	$195.25	$195.20
Purchase #6	$98.54	6.269%	$104.7175	$104.72	$104.70	$104.70
Purchase #7	$91.52	9.345%	$100.0725	$100.07	$100.05	$100.10
7 purchase totals =	$794.46		$870.9065	$870.90	$870.85	$870.90