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	$240.68	13.375%	$272.871	$272.87	$272.85	$272.90
Purchase #2	$110.43	5.746%	$116.7753	$116.78	$116.80	$116.80
Purchase #3	$51.38	4.112%	$53.4927	$53.49	$53.50	$53.50
Purchase #4	$82.86	10.164%	$91.2819	$91.28	$91.30	$91.30
Purchase #5	$84.36	7.647%	$90.811	$90.81	$90.80	$90.80
Purchase #6	$167.97	12.209%	$188.4775	$188.48	$188.50	$188.50
Purchase #7	$250.72	11.739%	$280.152	$280.15	$280.15	$280.20
7 purchase totals =	$988.40		$1,093.8614	$1,093.86	$1,093.90	$1,094.00