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	$248.25	10.104%	$273.3332	$273.33	$273.35	$273.30
Purchase #2	$234.41	13.184%	$265.3146	$265.31	$265.30	$265.30
Purchase #3	$79.66	6.243%	$84.6332	$84.63	$84.65	$84.60
Purchase #4	$93.54	12.517%	$105.2484	$105.25	$105.25	$105.20
Purchase #5	$78.47	3.202%	$80.9826	$80.98	$81.00	$81.00
Purchase #6	$237.67	9.201%	$259.538	$259.54	$259.55	$259.50
Purchase #7	$40.28	4.670%	$42.1611	$42.16	$42.15	$42.20
7 purchase totals =	$1,012.28		$1,111.2111	$1,111.20	$1,111.25	$1,111.10