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	$156.97	10.301%	$173.1395	$173.14	$173.15	$173.10
Purchase #2	$227.88	12.359%	$256.0437	$256.04	$256.05	$256.00
Purchase #3	$179.90	9.286%	$196.6055	$196.61	$196.60	$196.60
Purchase #4	$225.30	10.499%	$248.9542	$248.95	$248.95	$249.00
Purchase #5	$130.79	8.421%	$141.8038	$141.80	$141.80	$141.80
Purchase #6	$232.55	9.839%	$255.4306	$255.43	$255.45	$255.40
Purchase #7	$46.59	7.360%	$50.019	$50.02	$50.00	$50.00
7 purchase totals =	$1,199.98		$1,321.9963	$1,321.99	$1,322.00	$1,321.90