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	$26.79	5.244%	$28.1949	$28.19	$28.20	$28.20
Purchase #2	$250.41	12.741%	$282.3147	$282.31	$282.30	$282.30
Purchase #3	$159.50	7.763%	$171.882	$171.88	$171.90	$171.90
Purchase #4	$68.35	4.566%	$71.4709	$71.47	$71.45	$71.50
Purchase #5	$230.86	12.126%	$258.8541	$258.85	$258.85	$258.90
Purchase #6	$196.35	10.328%	$216.629	$216.63	$216.65	$216.60
Purchase #7	$233.90	3.616%	$242.3578	$242.36	$242.35	$242.40
7 purchase totals =	$1,166.16		$1,271.7034	$1,271.69	$1,271.70	$1,271.80