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	$6.79	10.718%	$7.5178	$7.52	$7.50	$7.50
Purchase #2	$53.32	11.644%	$59.5286	$59.53	$59.55	$59.50
Purchase #3	$106.37	9.534%	$116.5113	$116.51	$116.50	$116.50
Purchase #4	$147.84	13.296%	$167.4968	$167.50	$167.50	$167.50
Purchase #5	$131.67	12.703%	$148.396	$148.40	$148.40	$148.40
Purchase #6	$166.27	8.590%	$180.5526	$180.55	$180.55	$180.60
Purchase #7	$224.88	11.591%	$250.9458	$250.95	$250.95	$250.90
7 purchase totals =	$837.14		$930.9489	$930.96	$930.95	$930.90