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	$230.48	11.352%	$256.6441	$256.64	$256.65	$256.60
Purchase #2	$78.77	9.109%	$85.9452	$85.95	$85.95	$85.90
Purchase #3	$39.98	11.241%	$44.4742	$44.47	$44.45	$44.50
Purchase #4	$91.32	13.174%	$103.3505	$103.35	$103.35	$103.40
Purchase #5	$243.64	9.487%	$266.7541	$266.75	$266.75	$266.80
Purchase #6	$20.63	11.676%	$23.0388	$23.04	$23.05	$23.00
Purchase #7	$218.47	9.165%	$238.4928	$238.49	$238.50	$238.50
7 purchase totals =	$923.29		$1,018.6997	$1,018.69	$1,018.70	$1,018.70