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	$78.96	4.451%	$82.4745	$82.47	$82.45	$82.50
Purchase #2	$93.31	9.489%	$102.1642	$102.16	$102.15	$102.20
Purchase #3	$68.78	12.341%	$77.2681	$77.27	$77.25	$77.30
Purchase #4	$107.73	11.227%	$119.8248	$119.82	$119.80	$119.80
Purchase #5	$23.92	13.326%	$27.1076	$27.11	$27.10	$27.10
Purchase #6	$154.54	11.621%	$172.4991	$172.50	$172.50	$172.50
Purchase #7	$8.48	4.549%	$8.8658	$8.87	$8.85	$8.90
7 purchase totals =	$535.72		$590.2041	$590.20	$590.10	$590.30