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	$45.95	6.622%	$48.9928	$48.99	$49.00	$49.00
Purchase #2	$168.34	10.130%	$185.3928	$185.39	$185.40	$185.40
Purchase #3	$54.85	4.653%	$57.4022	$57.40	$57.40	$57.40
Purchase #4	$163.55	4.825%	$171.4413	$171.44	$171.45	$171.40
Purchase #5	$79.37	13.123%	$89.7857	$89.79	$89.80	$89.80
Purchase #6	$242.55	3.685%	$251.488	$251.49	$251.50	$251.50
Purchase #7	$104.69	12.115%	$117.3732	$117.37	$117.35	$117.40
7 purchase totals =	$859.30		$921.8760	$921.87	$921.90	$921.90