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	$219.76	13.760%	$249.999	$250.00	$250.00	$250.00
Purchase #2	$80.80	5.857%	$85.5325	$85.53	$85.55	$85.50
Purchase #3	$153.37	8.642%	$166.6242	$166.62	$166.60	$166.60
Purchase #4	$200.83	10.740%	$222.3991	$222.40	$222.40	$222.40
Purchase #5	$154.64	9.665%	$169.586	$169.59	$169.60	$169.60
Purchase #6	$239.89	13.809%	$273.0164	$273.02	$273.00	$273.00
Purchase #7	$216.65	10.424%	$239.2336	$239.23	$239.25	$239.20
7 purchase totals =	$1,265.94		$1,406.3908	$1,406.39	$1,406.40	$1,406.30