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	$31.48	10.153%	$34.6762	$34.68	$34.70	$34.70
Purchase #2	$58.84	12.729%	$66.3297	$66.33	$66.35	$66.30
Purchase #3	$53.94	10.376%	$59.5368	$59.54	$59.55	$59.50
Purchase #4	$207.63	10.586%	$229.6097	$229.61	$229.60	$229.60
Purchase #5	$42.46	7.871%	$45.802	$45.80	$45.80	$45.80
Purchase #6	$156.47	5.663%	$165.3309	$165.33	$165.35	$165.30
Purchase #7	$203.57	8.284%	$220.4337	$220.43	$220.45	$220.40
7 purchase totals =	$754.39		$821.7190	$821.72	$821.80	$821.60