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	$99.82	3.474%	$103.2877	$103.29	$103.30	$103.30
Purchase #2	$250.95	5.453%	$264.6343	$264.63	$264.65	$264.60
Purchase #3	$160.86	5.195%	$169.2167	$169.22	$169.20	$169.20
Purchase #4	$18.87	8.632%	$20.4989	$20.50	$20.50	$20.50
Purchase #5	$67.77	13.742%	$77.083	$77.08	$77.10	$77.10
Purchase #6	$82.68	8.366%	$89.597	$89.60	$89.60	$89.60
Purchase #7	$57.44	10.487%	$63.4637	$63.46	$63.45	$63.50
7 purchase totals =	$738.39		$787.7813	$787.78	$787.80	$787.80