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	$38.69	10.846%	$42.8863	$42.89	$42.90	$42.90
Purchase #2	$61.94	9.144%	$67.6038	$67.60	$67.60	$67.60
Purchase #3	$192.89	12.113%	$216.2548	$216.25	$216.25	$216.30
Purchase #4	$190.48	12.460%	$214.2138	$214.21	$214.20	$214.20
Purchase #5	$143.47	10.701%	$158.8227	$158.82	$158.80	$158.80
Purchase #6	$187.60	11.865%	$209.8587	$209.86	$209.85	$209.90
Purchase #7	$144.56	13.239%	$163.6983	$163.70	$163.70	$163.70
7 purchase totals =	$959.63		$1,073.3384	$1,073.33	$1,073.30	$1,073.40