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	$12.66	5.637%	$13.3736	$13.37	$13.35	$13.40
Purchase #2	$127.38	11.212%	$141.6618	$141.66	$141.65	$141.70
Purchase #3	$58.49	13.700%	$66.5031	$66.50	$66.50	$66.50
Purchase #4	$63.42	6.192%	$67.347	$67.35	$67.35	$67.30
Purchase #5	$211.56	5.545%	$223.291	$223.29	$223.30	$223.30
Purchase #6	$105.50	9.442%	$115.4613	$115.46	$115.45	$115.50
Purchase #7	$175.65	8.441%	$190.4766	$190.48	$190.50	$190.50
7 purchase totals =	$754.66		$818.1144	$818.11	$818.10	$818.20