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	$47.73	5.622%	$50.4134	$50.41	$50.40	$50.40
Purchase #2	$164.74	10.760%	$182.466	$182.47	$182.45	$182.50
Purchase #3	$173.29	13.374%	$196.4658	$196.47	$196.45	$196.50
Purchase #4	$71.30	9.259%	$77.9017	$77.90	$77.90	$77.90
Purchase #5	$62.78	6.150%	$66.641	$66.64	$66.65	$66.60
Purchase #6	$65.52	12.528%	$73.7283	$73.73	$73.75	$73.70
Purchase #7	$161.36	5.797%	$170.714	$170.71	$170.70	$170.70
7 purchase totals =	$746.72		$818.3302	$818.33	$818.30	$818.30