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	$14.46	13.361%	$16.392	$16.39	$16.40	$16.40
Purchase #2	$83.68	3.581%	$86.6766	$86.68	$86.70	$86.70
Purchase #3	$181.46	13.262%	$205.5252	$205.53	$205.55	$205.50
Purchase #4	$31.80	3.764%	$32.997	$33.00	$33.00	$33.00
Purchase #5	$35.80	6.308%	$38.0583	$38.06	$38.05	$38.10
Purchase #6	$187.31	4.695%	$196.1042	$196.10	$196.10	$196.10
Purchase #7	$75.94	4.124%	$79.0718	$79.07	$79.05	$79.10
7 purchase totals =	$610.45		$654.8251	$654.83	$654.85	$654.90