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	$37.52	5.164%	$39.4575	$39.46	$39.45	$39.50
Purchase #2	$177.63	10.522%	$196.3202	$196.32	$196.30	$196.30
Purchase #3	$115.49	3.654%	$119.71	$119.71	$119.70	$119.70
Purchase #4	$86.34	6.187%	$91.6819	$91.68	$91.70	$91.70
Purchase #5	$229.52	11.330%	$255.5246	$255.52	$255.50	$255.50
Purchase #6	$111.49	8.185%	$120.6155	$120.62	$120.60	$120.60
Purchase #7	$126.56	4.777%	$132.6058	$132.61	$132.60	$132.60
7 purchase totals =	$884.55		$955.9155	$955.92	$955.85	$955.90