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	$240.60	4.296%	$250.9362	$250.94	$250.95	$250.90
Purchase #2	$68.27	7.518%	$73.4025	$73.40	$73.40	$73.40
Purchase #3	$130.93	6.842%	$139.8882	$139.89	$139.90	$139.90
Purchase #4	$132.67	8.259%	$143.6272	$143.63	$143.65	$143.60
Purchase #5	$72.50	13.279%	$82.1273	$82.13	$82.15	$82.10
Purchase #6	$34.83	7.327%	$37.382	$37.38	$37.40	$37.40
Purchase #7	$45.32	10.364%	$50.017	$50.02	$50.00	$50.00
7 purchase totals =	$725.12		$777.3804	$777.39	$777.45	$777.30