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	$238.78	13.490%	$270.9914	$270.99	$271.00	$271.00
Purchase #2	$232.52	13.370%	$263.6079	$263.61	$263.60	$263.60
Purchase #3	$78.33	3.697%	$81.2259	$81.23	$81.25	$81.20
Purchase #4	$110.78	12.625%	$124.766	$124.77	$124.75	$124.80
Purchase #5	$81.98	7.577%	$88.1916	$88.19	$88.20	$88.20
Purchase #6	$109.81	6.110%	$116.5194	$116.52	$116.50	$116.50
Purchase #7	$244.34	4.396%	$255.0812	$255.08	$255.10	$255.10
7 purchase totals =	$1,096.54		$1,200.3834	$1,200.39	$1,200.40	$1,200.40