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	$207.98	9.627%	$228.0022	$228.00	$228.00	$228.00
Purchase #2	$116.34	6.332%	$123.7066	$123.71	$123.70	$123.70
Purchase #3	$54.51	13.141%	$61.6732	$61.67	$61.65	$61.70
Purchase #4	$232.69	3.541%	$240.9296	$240.93	$240.95	$240.90
Purchase #5	$185.30	5.676%	$195.8176	$195.82	$195.80	$195.80
Purchase #6	$25.77	6.210%	$27.3703	$27.37	$27.35	$27.40
Purchase #7	$47.47	13.538%	$53.8965	$53.90	$53.90	$53.90
7 purchase totals =	$870.06		$931.3960	$931.40	$931.35	$931.40