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	$249.47	7.256%	$267.5715	$267.57	$267.55	$267.60
Purchase #2	$64.31	9.656%	$70.5198	$70.52	$70.50	$70.50
Purchase #3	$80.47	12.329%	$90.3911	$90.39	$90.40	$90.40
Purchase #4	$85.37	8.655%	$92.7588	$92.76	$92.75	$92.80
Purchase #5	$41.42	7.366%	$44.471	$44.47	$44.45	$44.50
Purchase #6	$8.27	6.609%	$8.8166	$8.82	$8.80	$8.80
Purchase #7	$53.37	4.121%	$55.5694	$55.57	$55.55	$55.60
7 purchase totals =	$582.68		$630.0982	$630.10	$630.00	$630.20