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	$242.82	7.683%	$261.4759	$261.48	$261.50	$261.50
Purchase #2	$180.91	8.820%	$196.8663	$196.87	$196.85	$196.90
Purchase #3	$144.76	10.211%	$159.5414	$159.54	$159.55	$159.50
Purchase #4	$209.94	7.292%	$225.2488	$225.25	$225.25	$225.20
Purchase #5	$11.36	13.486%	$12.892	$12.89	$12.90	$12.90
Purchase #6	$216.44	8.612%	$235.0798	$235.08	$235.10	$235.10
Purchase #7	$230.81	4.198%	$240.4994	$240.50	$240.50	$240.50
7 purchase totals =	$1,237.04		$1,331.6036	$1,331.61	$1,331.65	$1,331.60