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	$23.64	4.244%	$24.6433	$24.64	$24.65	$24.60
Purchase #2	$80.94	3.506%	$83.7778	$83.78	$83.80	$83.80
Purchase #3	$92.71	11.592%	$103.4569	$103.46	$103.45	$103.50
Purchase #4	$92.89	5.866%	$98.3389	$98.34	$98.35	$98.30
Purchase #5	$124.73	9.737%	$136.875	$136.88	$136.90	$136.90
Purchase #6	$176.80	12.237%	$198.435	$198.44	$198.45	$198.40
Purchase #7	$178.51	5.628%	$188.5565	$188.56	$188.55	$188.60
7 purchase totals =	$770.22		$834.0834	$834.10	$834.15	$834.10