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	$38.36	11.377%	$42.7242	$42.72	$42.70	$42.70
Purchase #2	$227.57	3.185%	$234.8181	$234.82	$234.80	$234.80
Purchase #3	$225.31	13.483%	$255.6885	$255.69	$255.70	$255.70
Purchase #4	$12.97	12.449%	$14.5846	$14.58	$14.60	$14.60
Purchase #5	$141.99	11.857%	$158.8258	$158.83	$158.85	$158.80
Purchase #6	$78.47	13.692%	$89.2141	$89.21	$89.20	$89.20
Purchase #7	$33.61	12.729%	$37.8882	$37.89	$37.90	$37.90
7 purchase totals =	$758.28		$833.7435	$833.74	$833.75	$833.70