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	$144.83	3.735%	$150.2394	$150.24	$150.25	$150.20
Purchase #2	$45.35	3.194%	$46.7985	$46.80	$46.80	$46.80
Purchase #3	$191.88	10.538%	$212.1003	$212.10	$212.10	$212.10
Purchase #4	$99.30	13.336%	$112.5426	$112.54	$112.55	$112.50
Purchase #5	$236.80	13.725%	$269.3008	$269.30	$269.30	$269.30
Purchase #6	$248.32	6.239%	$263.8127	$263.81	$263.80	$263.80
Purchase #7	$33.58	5.672%	$35.4847	$35.48	$35.50	$35.50
7 purchase totals =	$1,000.06		$1,090.2790	$1,090.27	$1,090.30	$1,090.20