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	$166.36	3.771%	$172.6334	$172.63	$172.65	$172.60
Purchase #2	$242.73	12.519%	$273.1174	$273.12	$273.10	$273.10
Purchase #3	$93.30	8.230%	$100.9786	$100.98	$101.00	$101.00
Purchase #4	$57.89	3.140%	$59.7077	$59.71	$59.70	$59.70
Purchase #5	$80.55	7.445%	$86.5469	$86.55	$86.55	$86.50
Purchase #6	$36.58	5.401%	$38.5557	$38.56	$38.55	$38.60
Purchase #7	$162.58	10.576%	$179.7745	$179.77	$179.75	$179.80
7 purchase totals =	$839.99		$911.3142	$911.32	$911.30	$911.30