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	$19.73	8.168%	$21.3415	$21.34	$21.35	$21.30
Purchase #2	$55.83	13.693%	$63.4748	$63.47	$63.45	$63.50
Purchase #3	$99.83	4.277%	$104.0997	$104.10	$104.10	$104.10
Purchase #4	$135.61	6.824%	$144.864	$144.86	$144.85	$144.90
Purchase #5	$143.31	8.442%	$155.4082	$155.41	$155.40	$155.40
Purchase #6	$118.71	8.626%	$128.9499	$128.95	$128.95	$128.90
Purchase #7	$244.29	8.591%	$265.277	$265.28	$265.30	$265.30
7 purchase totals =	$817.31		$883.4151	$883.41	$883.40	$883.40