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	$39.84	3.665%	$41.3001	$41.30	$41.30	$41.30
Purchase #2	$209.62	3.680%	$217.334	$217.33	$217.35	$217.30
Purchase #3	$224.42	12.873%	$253.3096	$253.31	$253.30	$253.30
Purchase #4	$55.87	6.420%	$59.4569	$59.46	$59.45	$59.50
Purchase #5	$250.35	9.613%	$274.4161	$274.42	$274.40	$274.40
Purchase #6	$23.40	8.795%	$25.458	$25.46	$25.45	$25.50
Purchase #7	$12.56	4.676%	$13.1473	$13.15	$13.15	$13.10
7 purchase totals =	$816.06		$884.4220	$884.43	$884.40	$884.40