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	$89.89	12.273%	$100.9222	$100.92	$100.90	$100.90
Purchase #2	$70.97	10.254%	$78.2473	$78.25	$78.25	$78.20
Purchase #3	$200.32	11.495%	$223.3468	$223.35	$223.35	$223.30
Purchase #4	$168.40	7.275%	$180.6511	$180.65	$180.65	$180.70
Purchase #5	$240.57	6.564%	$256.361	$256.36	$256.35	$256.40
Purchase #6	$36.74	5.545%	$38.7772	$38.78	$38.80	$38.80
Purchase #7	$156.98	13.684%	$178.4611	$178.46	$178.45	$178.50
7 purchase totals =	$963.87		$1,056.7667	$1,056.77	$1,056.75	$1,056.80