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	$158.94	8.219%	$172.0033	$172.00	$172.00	$172.00
Purchase #2	$161.88	5.833%	$171.3225	$171.32	$171.30	$171.30
Purchase #3	$202.25	8.234%	$218.9033	$218.90	$218.90	$218.90
Purchase #4	$208.90	11.806%	$233.5627	$233.56	$233.55	$233.60
Purchase #5	$35.52	12.110%	$39.8215	$39.82	$39.80	$39.80
Purchase #6	$209.97	9.310%	$229.5182	$229.52	$229.50	$229.50
Purchase #7	$96.65	7.179%	$103.5885	$103.59	$103.60	$103.60
7 purchase totals =	$1,074.11		$1,168.7200	$1,168.71	$1,168.65	$1,168.70