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	$175.61	12.515%	$197.5876	$197.59	$197.60	$197.60
Purchase #2	$74.96	4.678%	$78.4666	$78.47	$78.45	$78.50
Purchase #3	$122.68	4.792%	$128.5588	$128.56	$128.55	$128.60
Purchase #4	$97.79	12.250%	$109.7693	$109.77	$109.75	$109.80
Purchase #5	$64.86	12.384%	$72.8923	$72.89	$72.90	$72.90
Purchase #6	$180.99	6.790%	$193.2792	$193.28	$193.30	$193.30
Purchase #7	$31.39	9.151%	$34.2625	$34.26	$34.25	$34.30
7 purchase totals =	$748.28		$814.8163	$814.82	$814.80	$815.00