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	$181.41	4.555%	$189.6732	$189.67	$189.65	$189.70
Purchase #2	$86.65	13.817%	$98.6224	$98.62	$98.60	$98.60
Purchase #3	$42.50	11.217%	$47.2672	$47.27	$47.25	$47.30
Purchase #4	$58.90	5.389%	$62.0741	$62.07	$62.05	$62.10
Purchase #5	$38.55	10.548%	$42.6163	$42.62	$42.60	$42.60
Purchase #6	$82.68	12.166%	$92.7388	$92.74	$92.75	$92.70
Purchase #7	$102.59	7.146%	$109.9211	$109.92	$109.90	$109.90
7 purchase totals =	$593.28		$642.9131	$642.91	$642.80	$642.90