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	$17.76	4.470%	$18.5539	$18.55	$18.55	$18.60
Purchase #2	$211.30	12.160%	$236.9941	$236.99	$237.00	$237.00
Purchase #3	$152.47	12.651%	$171.759	$171.76	$171.75	$171.80
Purchase #4	$33.88	3.571%	$35.0899	$35.09	$35.10	$35.10
Purchase #5	$86.80	13.623%	$98.6248	$98.62	$98.60	$98.60
Purchase #6	$99.43	13.154%	$112.509	$112.51	$112.50	$112.50
Purchase #7	$80.78	6.831%	$86.2981	$86.30	$86.30	$86.30
7 purchase totals =	$682.42		$759.8288	$759.82	$759.80	$759.90