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	$230.96	8.657%	$250.9542	$250.95	$250.95	$251.00
Purchase #2	$150.53	11.836%	$168.3467	$168.35	$168.35	$168.30
Purchase #3	$150.68	13.205%	$170.5773	$170.58	$170.60	$170.60
Purchase #4	$174.33	4.625%	$182.3928	$182.39	$182.40	$182.40
Purchase #5	$88.77	7.684%	$95.5911	$95.59	$95.60	$95.60
Purchase #6	$163.32	6.234%	$173.5014	$173.50	$173.50	$173.50
Purchase #7	$50.30	13.192%	$56.9356	$56.94	$56.95	$56.90
7 purchase totals =	$1,008.89		$1,098.2991	$1,098.30	$1,098.35	$1,098.30