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	$30.34	10.699%	$33.5861	$33.59	$33.60	$33.60
Purchase #2	$57.31	3.499%	$59.3153	$59.32	$59.30	$59.30
Purchase #3	$64.89	11.716%	$72.4925	$72.49	$72.50	$72.50
Purchase #4	$167.46	12.154%	$187.8131	$187.81	$187.80	$187.80
Purchase #5	$210.82	5.213%	$221.81	$221.81	$221.80	$221.80
Purchase #6	$66.75	6.575%	$71.1388	$71.14	$71.15	$71.10
Purchase #7	$212.56	13.184%	$240.5839	$240.58	$240.60	$240.60
7 purchase totals =	$810.13		$886.7397	$886.74	$886.75	$886.70