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	$123.92	10.649%	$137.1162	$137.12	$137.10	$137.10
Purchase #2	$235.48	8.348%	$255.1379	$255.14	$255.15	$255.10
Purchase #3	$128.78	5.787%	$136.2325	$136.23	$136.25	$136.20
Purchase #4	$114.89	3.624%	$119.0536	$119.05	$119.05	$119.10
Purchase #5	$75.32	9.316%	$82.3368	$82.34	$82.35	$82.30
Purchase #6	$153.76	3.656%	$159.3815	$159.38	$159.40	$159.40
Purchase #7	$225.45	12.805%	$254.3189	$254.32	$254.30	$254.30
7 purchase totals =	$1,057.60		$1,143.5774	$1,143.58	$1,143.60	$1,143.50