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	$56.74	3.183%	$58.546	$58.55	$58.55	$58.50
Purchase #2	$40.49	4.717%	$42.3999	$42.40	$42.40	$42.40
Purchase #3	$179.80	9.505%	$196.89	$196.89	$196.90	$196.90
Purchase #4	$213.61	3.648%	$221.4025	$221.40	$221.40	$221.40
Purchase #5	$103.87	8.860%	$113.0729	$113.07	$113.05	$113.10
Purchase #6	$101.87	12.299%	$114.399	$114.40	$114.40	$114.40
Purchase #7	$217.30	6.514%	$231.4549	$231.45	$231.45	$231.50
7 purchase totals =	$913.68		$978.1652	$978.16	$978.15	$978.20