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	$90.49	5.293%	$95.2796	$95.28	$95.30	$95.30
Purchase #2	$136.93	6.161%	$145.3663	$145.37	$145.35	$145.40
Purchase #3	$52.81	9.637%	$57.8993	$57.90	$57.90	$57.90
Purchase #4	$35.88	10.271%	$39.5652	$39.57	$39.55	$39.60
Purchase #5	$46.97	6.405%	$49.9784	$49.98	$50.00	$50.00
Purchase #6	$22.49	13.592%	$25.5468	$25.55	$25.55	$25.50
Purchase #7	$137.32	7.614%	$147.7755	$147.78	$147.80	$147.80
7 purchase totals =	$522.89		$561.4111	$561.43	$561.45	$561.50