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	$72.68	13.459%	$82.462	$82.46	$82.45	$82.50
Purchase #2	$153.33	10.579%	$169.5508	$169.55	$169.55	$169.60
Purchase #3	$175.63	5.278%	$184.8998	$184.90	$184.90	$184.90
Purchase #4	$243.66	12.129%	$273.2135	$273.21	$273.20	$273.20
Purchase #5	$121.53	5.827%	$128.6116	$128.61	$128.60	$128.60
Purchase #6	$158.75	12.684%	$178.8859	$178.89	$178.90	$178.90
Purchase #7	$69.93	5.252%	$73.6027	$73.60	$73.60	$73.60
7 purchase totals =	$995.51		$1,091.2263	$1,091.22	$1,091.20	$1,091.30