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	$78.67	13.729%	$89.4706	$89.47	$89.45	$89.50
Purchase #2	$28.68	11.347%	$31.9343	$31.93	$31.95	$31.90
Purchase #3	$214.70	10.537%	$237.3229	$237.32	$237.30	$237.30
Purchase #4	$12.31	12.311%	$13.8255	$13.83	$13.85	$13.80
Purchase #5	$38.71	9.488%	$42.3828	$42.38	$42.40	$42.40
Purchase #6	$83.94	8.261%	$90.8743	$90.87	$90.85	$90.90
Purchase #7	$201.26	8.736%	$218.8421	$218.84	$218.85	$218.80
7 purchase totals =	$658.27		$724.6525	$724.64	$724.65	$724.60