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	$21.30	5.545%	$22.4811	$22.48	$22.50	$22.50
Purchase #2	$136.73	7.352%	$146.7824	$146.78	$146.80	$146.80
Purchase #3	$83.78	5.668%	$88.5287	$88.53	$88.55	$88.50
Purchase #4	$64.89	9.534%	$71.0766	$71.08	$71.10	$71.10
Purchase #5	$12.74	6.174%	$13.5266	$13.53	$13.55	$13.50
Purchase #6	$105.70	7.360%	$113.4795	$113.48	$113.50	$113.50
Purchase #7	$94.64	10.613%	$104.6841	$104.68	$104.70	$104.70
7 purchase totals =	$519.78		$560.5590	$560.56	$560.70	$560.60