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	$86.29	4.319%	$90.0169	$90.02	$90.00	$90.00
Purchase #2	$168.64	8.219%	$182.5005	$182.50	$182.50	$182.50
Purchase #3	$114.46	11.279%	$127.3699	$127.37	$127.35	$127.40
Purchase #4	$68.98	13.652%	$78.3971	$78.40	$78.40	$78.40
Purchase #5	$151.47	7.718%	$163.1605	$163.16	$163.15	$163.20
Purchase #6	$79.80	11.173%	$88.7161	$88.72	$88.70	$88.70
Purchase #7	$43.59	9.574%	$47.7633	$47.76	$47.75	$47.80
7 purchase totals =	$713.23		$777.9243	$777.93	$777.85	$778.00