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	$117.46	3.454%	$121.5171	$121.52	$121.50	$121.50
Purchase #2	$59.27	4.381%	$61.8666	$61.87	$61.85	$61.90
Purchase #3	$225.80	3.258%	$233.1566	$233.16	$233.15	$233.20
Purchase #4	$101.48	7.861%	$109.4573	$109.46	$109.45	$109.50
Purchase #5	$182.55	13.861%	$207.8533	$207.85	$207.85	$207.90
Purchase #6	$201.59	13.161%	$228.1213	$228.12	$228.10	$228.10
Purchase #7	$33.62	11.545%	$37.5014	$37.50	$37.50	$37.50
7 purchase totals =	$921.77		$999.4736	$999.48	$999.40	$999.60