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	$206.87	6.152%	$219.5966	$219.60	$219.60	$219.60
Purchase #2	$33.44	7.801%	$36.0487	$36.05	$36.05	$36.00
Purchase #3	$123.39	6.714%	$131.6744	$131.67	$131.65	$131.70
Purchase #4	$82.25	8.869%	$89.5448	$89.54	$89.55	$89.50
Purchase #5	$115.46	3.510%	$119.5126	$119.51	$119.50	$119.50
Purchase #6	$47.66	11.605%	$53.1909	$53.19	$53.20	$53.20
Purchase #7	$19.36	4.600%	$20.2506	$20.25	$20.25	$20.30
7 purchase totals =	$628.43		$669.8186	$669.81	$669.80	$669.80