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	$115.71	11.304%	$128.7899	$128.79	$128.80	$128.80
Purchase #2	$219.59	6.150%	$233.0948	$233.09	$233.10	$233.10
Purchase #3	$228.73	5.159%	$240.5302	$240.53	$240.55	$240.50
Purchase #4	$248.37	11.377%	$276.6271	$276.63	$276.65	$276.60
Purchase #5	$156.52	5.286%	$164.7936	$164.79	$164.80	$164.80
Purchase #6	$94.59	9.791%	$103.8513	$103.85	$103.85	$103.90
Purchase #7	$218.30	5.208%	$229.6691	$229.67	$229.65	$229.70
7 purchase totals =	$1,281.81		$1,377.3560	$1,377.35	$1,377.40	$1,377.40