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	$41.30	3.644%	$42.805	$42.81	$42.80	$42.80
Purchase #2	$83.92	6.751%	$89.5854	$89.59	$89.60	$89.60
Purchase #3	$200.31	3.849%	$208.0199	$208.02	$208.00	$208.00
Purchase #4	$120.25	6.535%	$128.1083	$128.11	$128.10	$128.10
Purchase #5	$10.91	5.835%	$11.5466	$11.55	$11.55	$11.50
Purchase #6	$194.87	12.615%	$219.4529	$219.45	$219.45	$219.50
Purchase #7	$190.67	4.320%	$198.9069	$198.91	$198.90	$198.90
7 purchase totals =	$842.23		$898.4250	$898.44	$898.40	$898.40