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	$165.97	8.257%	$179.6741	$179.67	$179.65	$179.70
Purchase #2	$129.45	9.406%	$141.6261	$141.63	$141.65	$141.60
Purchase #3	$180.36	13.779%	$205.2118	$205.21	$205.20	$205.20
Purchase #4	$227.76	5.470%	$240.2185	$240.22	$240.20	$240.20
Purchase #5	$38.39	10.148%	$42.2858	$42.29	$42.30	$42.30
Purchase #6	$96.82	3.151%	$99.8708	$99.87	$99.85	$99.90
Purchase #7	$192.41	4.205%	$200.5008	$200.50	$200.50	$200.50
7 purchase totals =	$1,031.16		$1,109.3879	$1,109.39	$1,109.35	$1,109.40