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	$17.55	5.642%	$18.5402	$18.54	$18.55	$18.50
Purchase #2	$103.63	5.629%	$109.4633	$109.46	$109.45	$109.50
Purchase #3	$250.46	4.817%	$262.5247	$262.52	$262.50	$262.50
Purchase #4	$228.35	11.152%	$253.8156	$253.82	$253.80	$253.80
Purchase #5	$238.32	4.402%	$248.8108	$248.81	$248.80	$248.80
Purchase #6	$79.41	13.750%	$90.3289	$90.33	$90.35	$90.30
Purchase #7	$157.45	11.771%	$175.9834	$175.98	$176.00	$176.00
7 purchase totals =	$1,075.17		$1,159.4669	$1,159.46	$1,159.45	$1,159.40