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	$47.30	10.481%	$52.2575	$52.26	$52.25	$52.30
Purchase #2	$42.43	5.148%	$44.6143	$44.61	$44.60	$44.60
Purchase #3	$136.57	10.112%	$150.38	$150.38	$150.40	$150.40
Purchase #4	$94.72	3.391%	$97.932	$97.93	$97.95	$97.90
Purchase #5	$118.41	4.338%	$123.5466	$123.55	$123.55	$123.50
Purchase #6	$116.64	8.829%	$126.9381	$126.94	$126.95	$126.90
Purchase #7	$188.79	10.782%	$209.1453	$209.15	$209.15	$209.10
7 purchase totals =	$744.86		$804.8138	$804.82	$804.85	$804.70