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	$160.84	4.690%	$168.3834	$168.38	$168.40	$168.40
Purchase #2	$36.36	9.285%	$39.736	$39.74	$39.75	$39.70
Purchase #3	$81.77	9.591%	$89.6126	$89.61	$89.60	$89.60
Purchase #4	$41.47	7.517%	$44.5873	$44.59	$44.60	$44.60
Purchase #5	$159.80	13.614%	$181.5552	$181.56	$181.55	$181.60
Purchase #6	$226.60	5.277%	$238.5577	$238.56	$238.55	$238.60
Purchase #7	$33.45	9.596%	$36.6599	$36.66	$36.65	$36.70
7 purchase totals =	$740.29		$799.0921	$799.10	$799.10	$799.20