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	$210.88	6.558%	$224.7095	$224.71	$224.70	$224.70
Purchase #2	$171.45	8.700%	$186.3662	$186.37	$186.35	$186.40
Purchase #3	$170.52	8.407%	$184.8556	$184.86	$184.85	$184.90
Purchase #4	$203.29	8.188%	$219.9354	$219.94	$219.95	$219.90
Purchase #5	$96.39	3.209%	$99.4832	$99.48	$99.50	$99.50
Purchase #6	$24.93	6.171%	$26.4684	$26.47	$26.45	$26.50
Purchase #7	$142.53	11.241%	$158.5518	$158.55	$158.55	$158.60
7 purchase totals =	$1,019.99		$1,100.3701	$1,100.38	$1,100.35	$1,100.50