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	$99.94	3.654%	$103.5918	$103.59	$103.60	$103.60
Purchase #2	$139.42	4.295%	$145.4081	$145.41	$145.40	$145.40
Purchase #3	$157.64	12.140%	$176.7775	$176.78	$176.80	$176.80
Purchase #4	$12.77	3.837%	$13.26	$13.26	$13.25	$13.30
Purchase #5	$221.63	3.488%	$229.3605	$229.36	$229.35	$229.40
Purchase #6	$55.87	10.275%	$61.6106	$61.61	$61.60	$61.60
Purchase #7	$117.45	9.759%	$128.9119	$128.91	$128.90	$128.90
7 purchase totals =	$804.72		$858.9204	$858.92	$858.90	$859.00