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	$16.96	9.501%	$18.5714	$18.57	$18.55	$18.60
Purchase #2	$79.84	3.835%	$82.9019	$82.90	$82.90	$82.90
Purchase #3	$108.91	8.613%	$118.2904	$118.29	$118.30	$118.30
Purchase #4	$123.61	10.719%	$136.8598	$136.86	$136.85	$136.90
Purchase #5	$137.81	8.322%	$149.2785	$149.28	$149.30	$149.30
Purchase #6	$114.49	11.797%	$127.9964	$128.00	$128.00	$128.00
Purchase #7	$186.27	13.569%	$211.545	$211.55	$211.55	$211.50
7 purchase totals =	$767.89		$845.4434	$845.45	$845.45	$845.50