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	$228.94	13.386%	$259.5859	$259.59	$259.60	$259.60
Purchase #2	$182.73	3.349%	$188.8496	$188.85	$188.85	$188.80
Purchase #3	$227.56	12.405%	$255.7888	$255.79	$255.80	$255.80
Purchase #4	$54.33	5.761%	$57.46	$57.46	$57.45	$57.50
Purchase #5	$159.32	11.700%	$177.9604	$177.96	$177.95	$178.00
Purchase #6	$133.33	7.873%	$143.8271	$143.83	$143.85	$143.80
Purchase #7	$228.63	7.554%	$245.9007	$245.90	$245.90	$245.90
7 purchase totals =	$1,214.84		$1,329.3725	$1,329.38	$1,329.40	$1,329.40