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	$70.79	6.142%	$75.1379	$75.14	$75.15	$75.10
Purchase #2	$170.44	11.682%	$190.3508	$190.35	$190.35	$190.40
Purchase #3	$116.33	13.139%	$131.6146	$131.61	$131.60	$131.60
Purchase #4	$115.32	3.680%	$119.5638	$119.56	$119.55	$119.60
Purchase #5	$217.93	4.866%	$228.5345	$228.53	$228.55	$228.50
Purchase #6	$210.49	12.331%	$236.4455	$236.45	$236.45	$236.40
Purchase #7	$147.96	13.801%	$168.38	$168.38	$168.40	$168.40
7 purchase totals =	$1,049.26		$1,150.0271	$1,150.02	$1,150.05	$1,150.00