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	$22.41	9.660%	$24.5748	$24.57	$24.55	$24.60
Purchase #2	$133.25	7.711%	$143.5249	$143.52	$143.50	$143.50
Purchase #3	$80.32	12.411%	$90.2885	$90.29	$90.30	$90.30
Purchase #4	$109.83	12.432%	$123.4841	$123.48	$123.50	$123.50
Purchase #5	$87.45	5.673%	$92.411	$92.41	$92.40	$92.40
Purchase #6	$115.98	10.165%	$127.7694	$127.77	$127.75	$127.80
Purchase #7	$215.86	7.354%	$231.7343	$231.73	$231.75	$231.70
7 purchase totals =	$765.10		$833.7870	$833.77	$833.75	$833.80