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	$198.42	12.687%	$223.5935	$223.59	$223.60	$223.60
Purchase #2	$44.66	4.205%	$46.538	$46.54	$46.55	$46.50
Purchase #3	$16.41	7.441%	$17.6311	$17.63	$17.65	$17.60
Purchase #4	$77.29	6.438%	$82.2659	$82.27	$82.25	$82.30
Purchase #5	$52.32	13.132%	$59.1907	$59.19	$59.20	$59.20
Purchase #6	$36.30	11.823%	$40.5917	$40.59	$40.60	$40.60
Purchase #7	$214.65	10.625%	$237.4566	$237.46	$237.45	$237.50
7 purchase totals =	$640.05		$707.2675	$707.27	$707.30	$707.30