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	$39.86	3.813%	$41.3799	$41.38	$41.40	$41.40
Purchase #2	$244.27	4.530%	$255.3354	$255.34	$255.35	$255.30
Purchase #3	$243.96	5.273%	$256.824	$256.82	$256.80	$256.80
Purchase #4	$13.79	11.473%	$15.3721	$15.37	$15.35	$15.40
Purchase #5	$220.62	5.700%	$233.1953	$233.20	$233.20	$233.20
Purchase #6	$147.90	7.236%	$158.602	$158.60	$158.60	$158.60
Purchase #7	$242.80	6.339%	$258.1911	$258.19	$258.20	$258.20
7 purchase totals =	$1,153.20		$1,218.8998	$1,218.90	$1,218.90	$1,218.90