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	$12.44	6.783%	$13.2838	$13.28	$13.30	$13.30
Purchase #2	$29.39	6.420%	$31.2768	$31.28	$31.30	$31.30
Purchase #3	$160.35	7.779%	$172.8236	$172.82	$172.80	$172.80
Purchase #4	$246.35	9.797%	$270.4849	$270.48	$270.50	$270.50
Purchase #5	$143.45	6.266%	$152.4386	$152.44	$152.45	$152.40
Purchase #6	$181.71	5.430%	$191.5769	$191.58	$191.60	$191.60
Purchase #7	$95.41	3.874%	$99.1062	$99.11	$99.10	$99.10
7 purchase totals =	$869.10		$930.9908	$930.99	$931.05	$931.00